History of Geophysical Research in The Netherlands ... - DWC - KNAW

History of Geophysical Research in The Netherlands
and its former Overseas Territories

Verhandelingen der Koninklijke Nederlandse Akademie van Wetenschappen,
Afdeling Natuurkunde, Eerste Reeks, Deel 32
History of Geophysical Research
in The Netherlands and its
former Overseas Territories
J. Veldkamp
North-Holland Publishing Company, Amsterdam/Oxford/New York, 1984

ISBN 0-4448-5615-3
Author's address: Prof. Dr. J. Veldkamp, Bosuillaan 8,
3722 XN Bilthoven, The Netherlands

Contents
Preface 8
Acknowledgements 9
Chapter I
Section 1.1
Section 1.2
Section 1.3
Research in Geomagnetism 11
Introduction 11
Geomagnetism in the Netherlands 12
Disturbances in the earth's magnetic field caused by the
sun 17
Section 1.4 Geomagnetism and the ionosphere 22
Section 1.5 Geomagnetism and cosmic rays 27
Section 1.6 Geomagnetic research in the former Netherlands East
Indies 29
Section 1.7 Geomagnetic research by Dutch scientists outside the
Netherlands and the Netherlands East Indies 31
Section 1.8 Geomagnetic research at sea 32
Section 1.8.1 Suriname: continental shelf (OCPS) 32
Section 1.8.2 Atlantic Ocean: NA V ADO Project 32
Section I. 8. 3 Atlantic Ocean: Kroonvlag Project 34
Section I. 8. 4 Atlantic Ocean: Vaarplan Projects 34
Section 1.8.5 Atlantic Ocean: other subjects 37
Section 1.9 Palaeomagnetic research 37
Section 1.9.1 Palaeomagnetism at the State University of Utrecht 40
Section 1.9.2 Palaeomagnetism at the Municipal University of Amsterdam
46
References to Chapter I 46
Chapter 11
Section 11. 1
Section 11.2
Section 11. 2. 1
Section 11. 2. 2
Section 11. 3
Section 11. 3. 1
Section 11. 3. 2
Section 11. 3. 3
Seismological Research
Seismological instrumentation
Seismological research in the Netherlands
Work of J. G. J . Scholte
Research by N.J. Vlaar and co-workers
Earthquake mechanisms
Research by A. R. Ritsema and others
Work of J .A. Steketee
Results of research in earthquake mechanisms
5
55
55
57
59
59
61
62
63
63

Section 11.3.3.1 Southeast Asia and Hindu Kush 63
Section 11.3.3.2 Europe 64
Section 11.4. 1 Seismicity of· the Mediterranean region 67
Section 11.4.2 Seismicity of the Netherlands 67
Section 11.5 Nuclear explosions 67
Section 11.6 Seismological research in the former Netherlands East
Indies 67
Section 11.6.1 Instrumentation at the KMMO 69
Section 11.6.2 Research results 69
Section 11.7. Seismological research at sea 71
Section 11.7.1 North Sea 71
Section 11.7.2 NAVADO Project - 1964 and 1965 71
Section 11.7.3 Suriname 72
Section 11.7.4 Kroonvlag Project: 1967 -1980 72
Section 11.7.5 Vaarplan Projects: 1974-1978 and 1978-1982 75
Section 11.7.6 Disposal of radioactive waste 75
References to Chapter 11 76
Chapter 111 Research in gravity 83
Section 111.1 The life work of F. A. Vening Meinesz - Gravity Surveys 83
Section 111.2 Downbuckling theory of Vening Meinesz 86
Section 111.3 Vening Meinesz and the theory of Wegener 88
Section 111.4 Importance of Vening Meinesz 88
Section 111.5 Gravity research by others 89
Refererences to Chapter 111 93
Chapter IV Geophysical activity in international relations 97
Section IV.1 Polar Years 97
Section IV. 2 Geophysical Years 99
Section IV. 3 Belgian-Netherlands Antarctic Expeditions 103
Section IV.4 The Upper Mantle Project (UMP) 106
Section IV. 5 The Geodynamics Project (GP) 106
Section IV. 6 Wind measurements in the ionosphere above Suriname
(September 1965) 109
References to Chapter IV 110
Chapter V
Section V.1
Section V. 2
Section V. 3
Section V. 4
Section V. 4.1
Section V. 4. 2
Section V. 4. 3
Section V. 5.
Section V. 5. 1
Section V. 5.2
Exploration Geophysics 112
Introduction 112
Geophysical investigations in the former Netherlands East
Indies 113
Geophysical exploration in Suriname 113
Geophysical surveys in the Netherlands 114
Gravity research in the southeast Netherlands by
Government Agencies 114
Mining possibilities in the Peel Field (North Brabant) 114
Geophysical survey in the province of Limburg 115
Geophysical exploration in the Netherlands by Oil Companies
- 115
Discovery of the Schoonebeek oil field 115
Discovery of the Groningen gas field 118
6

Section V. 5.3 Geophysical research at the KSEPL (Rijswijk. South
Holland) 118
Section V. 5.4 Exploration of the North Sea continental shelf 119
Section V . 6. Hydrogeological research in the Netherlands 119
Section V. 6.1 Water supplies 119
Section V. 6. 2 Geothermal energy 120
Section V. 7. Exploration geophysics at the University of Technology
(TH) at Delft 121
Section V. 7.1 Geoelectrical research by o. Koefoed and co-workers 121
Section V. 7.2 Electromagnetic sounding research by o. Koefoed and coworkers
122
Section V. 8.1 Seismological research at the TH of Delft by o. Koefoed
and co-workers 123
Section V. 8. 2 Seismological research by A. T. de Hoop and co-workers 123
Section V . 8.3 Research into seismic data processing by A. J. Berkhout
and co-workers 126
Section V. 8. 4 Processing of gravity data at the TH. Delft 127
Section V. 9 Exploration geophysics in the State University of Leiden 127
Section V. 10 Exploration geophysics at Utrecht 128
References to Chapter V 128
Chapter VI
Section V I . 1
Section V I. 2
Section V I . 3
Section V I . 4
Section V I . 5
Section V I . 6
The Teaching of Solid Earth Geophysics
Teaching geophysics at the State University of Utrecht
Teaching geophysics at the Municipal University of
Amsterdam
Teaching geophysics at the State University of Leiden
Teaching geophysics at the University of Technology at
Delft
University Teachers of solid earth geophysics
Conclusion
7
135
135
136
136
136
137
138

Preface
During the Congress of the International Union of Geological Sciences, held in
1964 at New Delhi, a resolution was adopted in which the national committees were
asked to take steps to draw up the history of the geosciences in each participating
country.
The Royal Netherlands Academy of Arts and Sciences, which incorporates
the Netherlands Committee of Geological Sciences, invited its Geosciences Section
to set up a committee to write the historical development of the geosciences
in the Netherlands and its former Overseas Territories. This committee began
its work in 1974. The present author was asked to write the history of geophysics,
in which of course the relations with geology would be taken into account.
In this book the word "geophysics" means, in particular, the physics of the
solid earth, excluding the atmosphere and the oceans. This restriction is appropriate,
notwithstanding the fact that the atmosphere and the oceans play
their role in geological processes. But the history of geophysics, in the limitcd
sense of the word, has more to do with geology than meteorology and oceanography.
However, the division between the solid and the gaseous-liquid earth
cannot always be maintained. For example, certain variations in thc geomagnetic
field are caused by movements in the upper layers of the atmosphere. Therefore
the history of ionospheric research had also to be dealt with.
The order chosen for the subjects (geomagnetism, seismology, gravity, exploration)
was made according to the sequence in which these chapters appear
in the Netherlands geophysical research.
The author has decided to limit quotations from the very great number of
publications concerning Netherlands geophysics. For this reason the list of
literature is incomplete; nevertheless he has attempted to mention all important
publications and to discuss them very briefly.
The historica I account does not go beyond the year 1980. Publications that
appeared after 1980 are not included in the text (apart from a few exceptions) .
The illustrations have been selected from the publications discussed or have
been chosen in connection with them. In cases where they are not easily understandabie
, the fundamental meaning is indicated in the caption.
8

Acknowledgements
A preprint of this book (in Outch) has been issued by the Royal Netherlands
Meteorological Institute (KNMI; publication number 162).
I am very grateful to Or. and Mrs. Schregard us (Bilt hoven) and to Or. A. E .
Stevens (Canada) for carefully reading and correcting the English version of
the manuscript. Or. Stevens has not only improved the style of this book but
also its composition by the rearrangement of some chapters. Anne. thank you
very much!
I am also indebted to others. among whom Or. Visser (Nootdorp). who drew
my attention to omissions in the original version of the manuscript. I have tried
to comply with their wishes and remarks .
9
J. Veldkamp

CHAPTER I
Research in Geomagnetism
1.1. INTRODUCTION
Long ago and over many centuries science was dominated by the philosophy
of Aristoteles. For most scholastic scientists Aristoteles was the overwhelming
authority who had given the solution to many secrets of nature. However, in
the 16th century a new method of scientific research came into being. The
scientists no longer followed exclusively the great Greek philosopher, but acknowledged
the value of experiments and measurements. This new method of
scientific work began with astronomy, but was soon extented to other branches
of science, among others to the physics of the earth.
The first great step forward in geophysics was made by the Portugese navigator,
J. de Castro (1500-1548). During his voyages between Lisbon and Goa
he regularly read the deviation of his compasses with respect to the true North.
In this practical work he had in mind some hypotheses (Hooykaas, 1980) that
he hoped to confirm by his measurements, viz. that there exists an agonic meridian
(with deviation zero), and that this deviation (or declination ) increases
in relation to the distance from the agonic meridian, similarly to the east and
west, by an equal amount for an equal distance. If these hypotheses were
true, the important problem of determining geographic longitude at sea would
in principle be solved. However, the second hypothesis appeared to be false.
Whereas the geographic latitude at sea could be found by observations of the
sun, the geographic longitude presented more difficuities. It could not be calculated
from the declination of the compass; other methods were req uired.
An important study related to the magnetic properties of the earth was made
by the English physician, W. Gilbert (1540-1603) who published a book entitied:
"De Magnete et de magno magnete Telluro" (1600). Gilbert conducted experiments
with a sphericallodestone (terelIa) as a model of the magnetic earth and
applied iron needies to investigate the magnetic properties of this terelIa . The
needies showed the characteristics of the geomagnetic inclination , ranging from
90° at the poles of the terelIa to 0° at the equator. Gilbert concluded from these
experiments: magnus magnes ipse est globus terrestris (the Earth behaves
like a great magnet) . This was probably the first time that conclusions about
the earth's magnetism were drawn from experiments. Another English scientist.
F. Bacon (1561-1626). stressed the importance of collecting data on geomagnetism
all over the world, as weil as conducting experiments (Hooykaas, 1976).
Also in the Netherlands the interest in geophysics was directed to the magnetism
of the earth and to the compass and its properties as a most useful instrument
11

for navigation. The clergyman and geographer, P. Plancius (1552-1622), hoped
just as De Castro that the magnetism of the earth would provide a solution to
the problem of determining geographic longitude at sea.
Netherlands physicists like S. Stevin (1548-1620) and Chr. Huygens (1629-
1695) showed interest in the practical nature of geophysical problems. In his
book "Havenvinding" (finding the harbour) Stevin agreed with Plancius concerning
the theory of longitude determination. Huygens contributed to the true
solution of this problem by developing the theory of the pendulum as weil as by
inventing a clockwork suitable for use on ships. By doing so he furthered the
accuracy of the measurement of time and therefore of the determination of longitude
at sea.
In the centuries after the Golden Age (the 17th century) the interest in geomagnetism
was no longer focused mainly on the values of the field components
all over the world, but more on the temporary variations . For years some scientists
determined daily the direction of the geomagnetic field. However, a
continuous study of the earth's magnetism based on measurements at regular
times, began not earlier than the middle of the 19th century.
I. 2. GEOMAGNETISM IN THE NETHERLANDS
In the Netherlands in the 19th century research into geophysics of the solid
earth was closely connected with meteorology and oceanography. When in 1854
the Royal Netherlands Meteorological Institute (KNMI) was founded at Utrecht,
meteorological research was put on a firm footing. The Institute was housed in
the Sonnenborgh, an old castle in the town of Utrecht (now the Astronomical
Observatory of the State University at Utrecht). In this building also ob servations.
of the earth's magnetic field were included in the routine of daily observations.
Three times a day the position of a magnetic needie on a scale was
re ad through a telescope in the cellar of the Sonnenborgh. These daily observations
of the declinations of the compass had started in 1849 (see: KNMI,
Gedenkboek, 1954).
The special interest in geomagnetism was coupled in the Netherlands (and in
other countries) with a general interest in the unknown and mysterious polar
regions , which in the last century were the aim of many expeditions (see: section
IV.l. Polar Years). Arelation bet ween geomagnetic storms and aurora was
known, but geomagnetism as weU as the aurora were not weU understood natural
phenomena. The connection between them and the relation with the polar
regions and with the activity of the sun were very puzzling. Therefore, regular
observations of the magnetic field of the earth we re considered to be worthwhile.
Several times a day two components of the geomagnetic field, the declination
and the horizontal force, were determined. In that way some knowledge
was gained about the regular variations of these quantities; and also of the
variations , later called magnetic storms, which are related to the appearance
of spots on the sun.
Photographic recording of geomagnetic variations began in 1868 in the cellar
of the Sonnenborgh, and since that time absolute measurements of the field
strength were also carried out, in conformity with international methods. In
the Yearbook of the KNMI of 1894 we find for the first time tables of hourly
values of the declination and of the horizontal intensity of the earth 's magtletic
field (KNMI, 1894).
The increased research activity in the field of geomagnetism. as appears from
the extensive KNMI publication of 1894, was due to the work of E. van Rijckevorsel,
who carried out measurements of declination , inclination and horizont al
12

intensity at more than 300 places in the Netherlands in the years 1889 to 1892
(Van Rijckevorsel, 1895). The geomagnetic field in the Netherlands appeared
to be somewhat disturbed. The local disturbances suggested arelation with
geological structures beneath the earth 's surface .
It had been known for many years that the declination of the compass varied
from place to place. As noted above, sailors had even hoped to use this deviation
to determine geographic longitude at sea, but this appeared to be impossible.
In this connection W. van Bemmelen must be mentioned. He devoted his
Ph.D. thesis to the isogones of the declination in the 16th and 17th century,
making use of ship's journals of the East Indian Company (Van Bemmelen, 1893).
The journals describe 38 voyages bet ween the Netherlands and the East Indies,
during which about 1000 measurements of the declination were carried out by
ship 's officers who did not fail to determine the deviation of their compass,
whenever and wherever possible. In continuation of this thesis he wrote a
treatise on the secular changes in the geomagnetic field in the years 1500 to
1850 (Van Bemmelen, 1897). The outcome of the measurements was presented
by Van Bemmelen in world maps with isogones for the years 1540, 1580, 1610,
1640, 1665 and 1680. He edited observations of the geomagnetic declination made
in the 18th century by P. van Musschenbroek (1729 to 1758) and by J. H. van
Swinden (1770 to 1780), (Van Bemmelen, 1892). He carried out measurements
in 1896 and 1897 in Switzerland together with Van Rijckevorsel, to see how the
earth's magnetic field depended on elevation , however, without suçcess (Van
Rijckevorsel and Van Bemmelen, 1899).
Figure 2. The Sonnenborgh in Utrecht, from 1854 to 1898 the site of the KNMI and
for the present the Astronomical Observatory of the State University at Utrecht.
13

In the course of time geomagnetic recordings in the Sonnenborgh became more
and more disturbed. Especially perambulators, which were pushed through the
park, were a nuisance. At first they could be kept at a safe distance by means
of a thorn hedge, but near the end of the century a quieter place had to be
found. Therefore, geomagnetic recording was moved in 1898 from the Sonnenborgh
in Utrecht to the manor Koelenberg at De Bilt (in the grounds of the
present KNMI). A description of the geomagnetic instruments and buildings in
these new grounds can be found in the publication "Mededelingen en Verhandelingen
van het KNMI" lA, and also in Yearbook-B, 1915.
Only for a decade the recordings were there free from artificial disturbances .
Then electrification of the former horse-drawn tramway, Utrecht-De Bilt-Zeist,
which was completed in 1909, caused problems. The tramway used direct current;
as a consequence magnetic disturbances were caused by the currents
flowing through the overhead wire and the rails, as weIl as by stray currents
that expanded from the rails over great distances and disturbed the natural
geomagnetic field. A great but temporary improvement was achieved by the
use of a second overhead wire (in 1911), which carried the return current instead
of the rails.
However, the situation again worsened. In 1938 the greater part of the network
of the Netherlands Railways was electrified. Direct current was used,
just as for the tramway, but of much greater strength . The only solution was
to move the geomagnetic observatory. A suitable site was found in the hamiet
of Witteveen (between Westerbork, Emmen and Hoogeveen in the province of
Drenthe). In the middle of 1938 a new observatory was put into use. A description
of the instruments with pictures of the buildings is given in KNMI-Yearbook
Geomagnetism, 1939. Until 1952 recordings of the geomagnetic variations
in the Magnetic Observatory at Witteveen were ideal. In May 1952 the Zwolle­
Groningen railway was electrified and this ended the period at Witteveen in
which no artificial disturbances occurred. Since 1952 instruments in the Magnetic
Observatory at Witteveen can no longer record in the finest details the
natural variations of the geomagnetic field.
The results of the recordings made by the KNMI have been published since
1903. From 1903 to 1938 the hourly values of the geomagnetic components were
derived from the records at De Bilt, and since 1938 the hourly means of the
components recorded at Witteveen . They have been published in the Yearbooks
of the KNMI (KNMI, 1903 to the present).
The possibility of carrying out field measurements with improved instruments
made a repetition of the magnetic survey of 1891 attractive. In the years 1942
to 1948 the geomagnetic field of the Netherlands was measured at about 400
places. The results have been published by J. Veldkamp in a KNMI publication
(Veldkamp , 1951). The anomalies of the geomagnetic field are related to the
subsurface structure in this country. This fact was established also by Ph.e.p.
Hartmann in his doctor's thesis (Hm'tmann. 1945), which was based on the geomagnetic
survey of 1942-1948, and on the geological knowledge at that time.
J.A. As analyzed secular variations (the slow variations that occurred in the
geomagnetic field during the last decades) and drew conciusions with respect
to future variations (As, 1967). The secular variations appear to be strongest
in some beits around the world that coincide more or less with the global tectonic
belts. J. A. As surmised that in these belts processes in the earth 's core
are linked with those in the mantIe of the earth (As, 1975).
In the period from 1960 to the present modern instruments have been devised
and constructed at the KNMI for measuring the earth 's magnetic field and its
components, such as proton magnetometers (also for use at sea) and a proton
vectormagnetometer as an observatory instrument. J.A. As also developed in-
15

....
Ol
Figure 4. The KNMI during the expansion in 1952. Arrows indicate. from left to right.
the seismograph pavilion. the building for geomagnetic measurements and the pavilion
for the variometers (Photo KLM Aerocarto).

struments for digitizing the components of the geomagnetic field. by using
proton magnetometers and fluxgate instruments (As. 1973). These modern instruments
are now in operation in the Magnetic Observatory at Witteveen . They
make it possible to calculate and to publish the geomagnetic values almost automatically.
I. 3. DISTURBANCES IN THE EARTH'S MAGNETIC FIELD CAUSED
BY THE SUN
Since the beginning the Netherlands have played an important role internationally
in characterizing the days from a geomagnetic viewpoint . The earth 's
magnetic field is quiet on some days and disturbed on others. The occurrence
of disturbances is related to the phenomenon of sunspots. These disturbances
are much stronger at higher than at lower latitudes; agiobal collection of data
is necessary to study them. M. Snellen. a member of the scientific staff of the
KNMI. was the first to collect. by request of the International Commission of
Terrestrial Magnetism. a commission of the International Union of Geodesy and
Geophysics (IUGG). geomagnetic character figures (0 = undisturbed day. 1 =
Figure 5. The Geomagnetic Observatory of the KNMI at Witteveen • a house without
windows (Photo J . B. van der Kolk. Naarden).
17

Geomagnetic Observatories and Surveys - Nether/ands . 1849 to 1980
Year Location Remarks
1849 Utrecht First geomagnetic observatory. measurements
several times daily
1868 Utrecht Continuous recording began
1889 to 1892 More than 300 places First geomagnetic survey of country
1898 De Bilt Geomagnetic observatory moved from
Utrecht
1938 Witteveen Geomagnetic observatory moved from
De Bilt
1942 to 1948 More than 400 places Second geomagnetic survey of country
moderately disturbed,2 = strongly disturbed day) from about 40 geomagnetic
observatories all over the world. He determined an international disturbanceindex
C from these data. Af ter his death in 1907 his work was continued by
G. van Dijk, who succeeded in extending the series of C-figures, which originally
began in 1906, back to 1890.
As the disturbance-index C had no quantitative value, the International Association
of Geomagnetism and Aeronomy (IAGA) of the IUGG decided to introduce
in 1939 a 3-hourly amplitude index, in order to express the degree of
disturbance in a quantitative manner. This quantification is necessary if one
wishes to study the relations between phenomena on the sun and in the high
atmosphere on the one hand and the transient disturbances in the earth's magnetic
field on the other. It is now possible to survey these relations over a
long series of years.
In the first IUGG conference af ter the war, in 1948, the KNMI was designated
anew as the international centre for the characterization of geomagnetic disturbances.
Compilation of character figures and special geomagnetic disturbances
(sudden commencements of magnetic storms and solar flare effects) was
consigned to J. Veldkamp . These geomagnetic data have been compiled and
published by the KNMI in an uninterrupted series of yearly IAGA-Bulletins,
from 1947 up to the present (IA GA , 1949-present). Since 1969 compilation and
editing of "Geomagnetic Data" has been done by D. van Sabben.
J. Ve/dkamp (1960) and J. G. J . Sc holte (1960) studied special disturbances of
the geomagnetic field, such as "giant pulsations"; these are harmonic vibrations
of the earth 's magnetic field ascribed to magneto-ionic disturbances that flow
back and forth along the lines of magnetic force between the northern and
southern hemispheres. They also wrote some papers on "solar flare effects" ,
geomagnetic disturbances caused by outbursts of ultraviolet light on the sun
(Ve/dkamp and Scho/te, 1954). The electric potentials and currents in the earth
that arecoupled to the magnetic variations by induction were investigated by
means of records obtained in the Magnetic Observatory at Witteveen . In view
of the very long wavelength of the geomagnetic disturbances a theory was developed
for the induction of geomagnetic and geoelectric fields in a spherical
earth (Scho/te and Ve/dkamp, 1955).
Veldkamp investigated with D. van Sabben (1959) the geomagnetic records of
some solar flare effects (s.f.e.) and reached the conclusion that the electric
currents that cause these magnetic disturbances (the s.f.e.) must flow in the
D-layer of the ionosphere (Le., at a height of 80 to 100 km).
19

Figure 7. Vector proton magnetometer (design J . A. As, 1973) in the Geomagnetic Observatory
at Witteveen. Courtesy of KNMI.
20

Figure 8. Geomagnetic anomalies in the Netherlands . Grey are positive regions (too
large values of the vertical component). white are negative regions (too sm all values).
The vectors indicate direction and magnitude of the horizontal deviations (Veldkamp •
1951). Courtesy of Bureau "Atlas of the Netherlands. 1963-1977".
21

Van Sabben has applied himself to the investigation of the electric current
systems in the ionosphere that are responsible for the diurnal variation of the
earth 's magnetic field. He proved that not only the tidal ionospheric winds but
also non- periodic ionospheric winds can produce these current systems (Van
Sabben, 1962) . Analysis of a great number of s.f.e. 's and of the diurnal variation
demonstrated that the patterns of variations in the northern and southern
hemispheres show a systematic displacement bet ween them (Van Sabben, 1961,
1964, 1968). This asymmetry points to the existence of currents along the magnetic
field lines connecting the northern with the southern ionosphere via the
magnetosphere. Even during the equinox the currents through the magnetosphere
can be comparable with the ionospheric currents (Van Sabben, 1966,
1969, 1970).
1. 4. GEOMAGNETISM AND THE IONOSPHERE
The transient geomagnetic variations , the regular as weU as the irregular,
are caused by electric currents in the ionosphere. Therefore, research into
the earth's magnetic field cannot be separated from a study of the high atmos-
Figure 9. Electric currents in the ionosphere, which cause the diurnal variation of
the geomagnetic field. The current pattern is due to daily tidal movements in the
ionosphere. The region bet ween the hatchings is the sunlit part of the ionosphere.
The dotted line denotes the geomagnetic equator. Current values must be multiplied
by 10.000 A. Situation on 21 September 1958 at 1.30 p.m. (Van Sabben, 1964).
22

phere. On the other hand, properties of the ionosphere are determined in great
part by the existence of the geomagnetic field in the ionospheric layers.
About 1920 some Dutch scientists, among whom the astronomer A. Pannekoek
(1926) and the physicist G. J. Elias (1923), made calculations on the formation
of ionization in the up per atmosphere, caused by the ultraviolet light of the
sun. Elias especiaUy studied the propagation of electromagnetic waves in a
partly ionized layer. Interest in the ionosphere was stimulated by the desirability
of having radio contact bet ween the Netherlands and its Colonies . Already
in 1923 a telegraphic connection had been made possible between Kootwijk
(Netherlands ) and Malabar (Java) using very long radio waves. Later on it
was shown that radio waves of relatively short wavelength were more suitable
for covering great distances, by means of reflections from the ionosphere.
Two scientists played a very important role in this field, viz. Balth. van der
Pol (University of Technology at Delft) and H. Bremmer (University of Technology
at Eindhoven). Both also worked with the Philips Research Laboratories
at Eindhoven.
Van der Pol carried out measurements of the electrical conductivity and the
dielectric constant of an ionized gas, as a model of the ionosphere. The influence
of a plasma on the propagation of radio waves was discussed in his doctor's
thesis (Van der Pol, 1920). His early work was devoted especially to the
mathematical aspects of radio science. However, upon his request, the program
of the Netherlands expedition at Angmagssalik (see: section IV.l. International
Polar Year, 1932-1933) also included soundings of the ionosphere at regular
times.
Bremmer , who joined Van der Pol's group, wrote many papers on tropospheric
and ionospheric propagation of radio waves. He also dealt with phenomena such
Figure 11. Sounding the ionosphere by reflection of radio waves of varying freq uency.
The time delay bet ween transmitted and reflected pulses determines the height of the
reflecting layer. By day three layers are present: the E-Iayer or Heaviside-Iayer,
and above it the Fl-1ayer and the F2-layer (or Appleton-Iayer). The frequency of
the reflected radio signa Is is a measure of the ionization at the height of reflection.
The magnetic double refraction of radio waves in the ionosphere is shown by repetition
of the Fl- and F2-reflections at higher frequencies (ionogram of KNMI, af ter Veldkamp,
1974; see also: Veldkamp and Scholte, 1954a).
24

as whistlers, ionospheric winds, tidal movements in the ionosphere and double
refraction of radio waves. Summaries of his work are given in his book "Terrestrial
Radio Waves: Theory of propagation" (Bremmer, 1949), and in the Encyclopaedia
of Physics: "Propagation of electromagnetic waves" (Bremmer, 1958).
Veldkamp , who had become director of the geophysical department of the
KNMI in 1945, believed that study of the highest atmospheric layers should be
included in the task of this Meteorological Institute, as weIl as continuous monitoring
of the troposphere and the stratosphere. Together with H.J. Groenewold
he commenced a regular study of the ionosphere in 1949 by means of a transmitter
and receiver made in the "Institut für Ionensphärenforschung" at Lindau
(Germany). After some years a new apparatus (with less mechanically moving
parts and therefore greater reliability) was constructed by H. J. A. Vesseur
(1977). Day and night the structure and the ionization of the ionosphere was
and still is recorded every half hour by means of this "ionosonde". The ionosp
here behaves like a mirror reflecting radio waves. Generally three layers
(E, Fl and F2) are present in the ionosphere above the Netherlands, at heights
of 110 km, 200 km and 300 km respectively. These layers are subject to regular
variations between day and night, and also to irregular variations due to the
activity of the sun.
The aim of the soundings is to monitor continuously the highest layers of
the atmosphere . The data acquired from the ionosphere are partly of purely
scientific and partly of practical importance. Groenewold (1948) wrote a paper
JANUARY 1970
Figure 12. Vector diagram of the wind in the E-layer of the ionosphere above De Bilt
(average diurnal variation in January 1970). A line from the origin to the point marking
a certain hour gives the average wind vector for that hour. The diagram shows
that the wind vector in the E-layer rotates twice per day. In addition the prevailing
wind is southwesterly during the whole day (Vesseur, 1977).
25
N

Ftgure 13. The changing ionosphere above De Bilt, over 24 hours. The E-, Fl and F2-layers
are formed by radiation from the sun af ter sunrise (6.00 a.m.). In the early afternoon
the ionization reaches a maximum; this is shown by the long echo traces. During the night
(7.00 p.m. to 5.00 a.m.) little ionization remains (lonograms of KNMI, Veldkamp, 1974).

on the formation of the ionized layers, on the propagation of radio waves in
the ionosphere, and on prediction and selection of the most suitable frequencies
for covering a certain distance by radio. In a further paper (Groenewold,
1949) he discussed temporary variations in the ionization and the influence on
the ionosphere of outbursts on the sun. He published also a theoretical study
on the triple magnetic splitting of radio waves reflected in the F2-1ayer (Groenewold,1950).
Veldkamp and Scholte (1954a) also studied the magnetic double refraction of
electromagnetic waves in the ionosphere. They investigated the equatorial
electrojet in the ionosphere, as revealed by the analysis of solar flare effects ,
and explained some properties of the electrojet by the non-coincidence of the
geomagnetic and geographic equators (Veldkamp and Scholte, 1954). H.J.A.
Vesseur (1970) succeeded in inferring from the fading pattern of radio waves
reflected in the ionosphere the rhythmic tidal movements of air in the ionosphere,
which are responsible for the diurnal geomagnetic variation. The wind
movements in the E-layer are recorded almost continuously by an automatic
apparatus developed by Vesseur. He could determine the diurnal and the semidiurnal
period of the tidal movements in the E-layer above the Netherlands
over a period of years (Vesseur, 1972). A similar apparatus was set up near
Paramaribo (Suriname); it was in operation from January 1971 until September
1972.
H. Kelder (1975) investigated the influence of acoustic gravity waves on ion
density in the E-layer. The tidal movements are in fact strongly disturbed by
acoustic waves with a very long wavelength , which travel through the ionosphere
and the thermosphere (Kelder, 1976).
Temporary disturbances in the geomagnetic field, which are caused by "disturbed"
solar radiation - corpuscular as weIl as electromagnetic - penetrating
the outer layers of the atmosphere, are important for changing the reflecting
power of the ionosphere. For this reason study of the ionosphere is of practical
importance for radio propagation through the ionosphere (Vesseur, 1974).
The results of this research are published each month by the KNMI in an "Ionospheric
Bulletin". In this monthly publication are given, not only heights and
plasma freq uencies of the ionospheric layers, but also factors for calculating the
radio frequencies for covering a certain distance and further the ionospheric
and geomagnetic disturbance-indices, disturbances in the intensity of cosmic
radiation , intensity of radio radiation from the sun and summaries of special
phenomena of the solar radiation (KNMI, 1949 up to the present).
The monthly publication of the "Ionospheric Bulletin" by the KNMI gives
evidence of the close relation existing between the ionosphere, the earth's
magnetic field, cosmic radiation and phenomena on the sun.
1.5. GEOMAGNETISM AND COSMIC RAYS
About 1930 J. Clay (professor at the Technical University of Bandoeng from
1920 to 1929, and professor at the Municipal University of Amsterdam from 1929
to 1952) discovered that the geomagnetic field exerts an influence on cosmic
rays. During his voyages bet ween the Netherlands and the Netherlands East
Indies, Clay studied the intensity of cosmic radiation (at that time called ultraradiation)
. lt appeared that this very penetrating radiation depended on the
geomagnetic latitude. The intensity was minimal in the Gulf of Aden, which is
in the neighbourhood of the geomagnetic equator (Clay, 1932). From this the
corpuscular character of cosmic rays became evident; only electrically charged
particles can be influenced by the magnetic field of the earth. The latitude
27

effect discovered by Clay was confirmed among others by Prins (1933) during
a voyage from Amsterdam to Cape Town.
After being appointed to the Municipal University of Amsterdam, Clay and
co-wor kers continued the investigation of cosmic radiation . Whereas measurements
in the years 1927 to 1930 could be interpreted by the model of a geomagnetic
dipole, situated somewhat eccentrically with respect to the centre of the
earth, it appeared, during a voyage in 1935 through the Panama Canal to Chile,
that the quadrupole terms of the geomagnetic potential also affected the cosmic
radiation perceptibly. If these second-order terms are taken into account, the
geomagnetic effects are no longer symmetric with respect to the geomagnetic
eq uator. Also an east-west asymmetry was discovered in cosmic radiation; this
proved that the primary radiation was largely or wholly composed of positively
charged particles .
E. M. Bruins devoted his thesis (1938) to calculations of the intensity of cosmic
radiation in the geomagnetic field, assumed to be due to a dipole plus a
quadrupole. In this thesis attention is paid also to the influence of temporary
disturbances in the earth's magnetic field, especially to magnetic storms. The
ring current around the earth, which is formed during a magnetic storm according
to the theory of Störmer, must influence the cosmic radiation. From
variations in the intensity of cosmic rays Bruins drew the conclusion that the
ring current should be present at some earth's radii distance from the centre
of the earth.
The relation between geomagnetic disturbances and changes in cosmic radiation
was also the subject of the doctor's thesis of H. F. Jongen (1952). He
found strong evidence for asolar origin of at least part of the cosmic radiation .
After Clay's death Jongen continued recording the transient variations in cosmic
radiation. In 1979 these recordings came to an end.
The research of Clay and his co-workers was published in many articles and
in four doctor's theses. The results obtained up to 1948 have been summarized
in a booklet entitled: Cosmic Rays (Clay, 1948).
I. 6. GEOMAGNETIC RESEARCH IN THE FORMER NETHERLANDS EAST INDIES
When the famous naturalist, Alexander von Humboldt, discovered during his
journey through North and South America that the strength of the earth 's
magnetic field is variabie and strongly dependent on geographic latitude, he
tried everywhere to arouse interest for magnetic observations. He considered
the latitude dependence of the geomagnetic force as the most important result
of his journey through North and South America. On the occasion of a chance
meeting in Berlin in 1856 with the then Governor-General of the Netherlands
Indies, he succeeded in convincing him of the importance of magnetic and meteorological
observations. The consequence of this talk was that the then Minister
of Colonies asked advice of the Director-in-Chief of the KNMI (Ch.H.D.
Buys Ballot) who recommended founding an observatory at Batavia. He also
suggested a .capable observer, P.A. Bergsma, who left for Batavia in 1862 and
who became the first director of the Royal Magnetic and Meteorological Observatory
(KMMO) at Batavia (see : Van der Lith and Snelleman, 1919). In the sequence
Magnetic/Meteorological probably the influence of Von Humboldt can be
traced!
In 1866 Bergsma's observatory was in full operation in a rented villa, south
of Batavia. A long series of bulky Yearbooks bears witness to an intensive and
wide-rangingresearch, especially in the domain of meteorology (see f. i. KMMO,
1871). As for geomagnetism the declination of the magnetic needie was observed
29

netic survey in the East Indian Archipelago. He measured the declination , inclination
and horizontal intensity of the geomagnetic field at about 150 places
on the various islands. This work with maps of the magnetic components, reduced
to 1-1-1876, was published by the Royal Netherlands Academy of Arts
and Sciences (Van Rijckevorsel, 1879).
W. van Bemmelen (1909) repeated the magnetic survey of the East Indies in
the years 1903 to 1907. He studied the secular variation of the earth 's magnetic
field in the western part of the East Indian Archipelago, based on measurements
from the years 1900 to 1918 (Van Bemmelen, 1920). The phenomenon of
secular variation aroused special interest. The speed of the variations is so
great that it is difficult to ascribe them to tectonic movements in the earth 's
crust.
Repeating the geomagnetic measurements with intervals of some years became
therefore a matter of routine. In the years 1917 and thereafter members of the
staff of the KMMO made regular field trips to repeat the magnetic surveys at
many places on the islands . The instruments were not very different from those
used by Van Rijckevorsel, viz. a magnetometer-theodolite for measurements of
declination and horizontal intensity, and a dip circle or inclinatorium for measurements
of inclination. Co-workers of the KMMO who took part in the measuring
program were C. Braak, W. van Bemmelen, J. Voûte and S. W . Visser, and
later H.P. Berlage and M;W.F. Schregardus. Visser (1925) published new isomagnetic
maps of the whole Archipelago based on the measurements of Braak,
Van Bemmelen, Voûte and himself.
During the Geophysical Year 1957 -1958 a geomagnetic observatory was operated
at Hollandia (former Netherlands New Guinea). see Chapter IV, section 2.
Geomagnetic Observatories and Surveys - Netherlands East lndies, 1866 to 1949
Year Location
1866 Batavia
1874 to 1877 About 150 places
1883 Batavia
1899 Buitenzorg
1903 to 1907 Throughout the islands
1917 to 1942 Ditto
1925 Kuyper Island
1942 to 1945 Kuyper Island
1945 to 1949 Kuyper Island
Remarks
First geomagnetic observatory, measurements
several times daily
First geomagnetic survey
Continuous photographic recording
began
Geomagnetic observatory moved from
Batavia
Second geomagneticsurvey
Third geomagnetic survey
Geomagnetic observatory moved from
Buitenzorg
Recordings interrupted by war
Observatory closed in 1949
1.7. GEOMAGNETIC RESEARCH BY DUTCH SCIENTISTS OUTSIDE THE
NETHERLANDS AND THE NETHERLANDS EAST INDIES
Some years af ter his East Indian expedition (see section 1.6) Van Rijckevorsel
left for South America with his instruments. He measured the geomagnetic
31

Figure 16. The oceanographic research vessel H.Nl.M.S. Snellius (photo courtesyof
the Maritime History section of the Staff of the Netherlands Navy).

the North Sea and in the Atlantic Ocean. In the beginning especially the bathymetry
of the sea bottom was determined, but later on also the structure of the
sedimentary layers and the geomagnetic field. Soundings of the ocean bottom
by the Marine Geophysics Group are discussed in the chapter on seismic research,
and the gravimetric measurements in the chapter on gravity. Below a
summary of the geomagnetic research is given; the results were presented in
a series of publications and a number of doctor's theses.
In the years 1964 and 1965 the Royal Navies of Great Britain and the Netherlands
, in cooperation with the U. S. Naval Research Laboratory , carried out
extensive oceanographic research of the Atlantic Ocean under the name of
NAVADO Project (North Atlantic Vidal and Dalrymple Oceanography). At the
request of the organizing committee the Netherlands took part in the third
phase of this project by making available H. NI. M. S. Snellius. The Snellius
crossed the North Atlantic ten times, and made possible measurements in a
region between 22°N. and 49°N. latitude. Collette and his co-workers (R.A.
Lagaay, A.P. van Lennep, K.W. Rutten, J.A. Schouten, R.D. Schuiling, F.W.
Warnaars and C. H. van der Weijden) were responsible for the geomagnetic measurements,
making use of the proton magnetometer of the KNMI. Gravity measurements
were carried out by G. L. Strang van Hees and T. J . Poelstra (TH at
Delft). Recordings of the bathymetry, the geomagnetic field and the gravity
field have been published by the Hydrographer of the Royal Netherlands Navy
(Anonymous, 1967). The Netherlands Organization for the Advancement of Pure
Research (ZWO) gave ample financial aid.
During these voyages between Europe and America, Collette and his colleagues
tried to measure the heat flow at some places at the bottom of the Atlantic Ocean,
but these measurements were not completely successful (Collette et al., 1968).
I. 8. 3. Atlantic Ocean: Kroonvlag Project
The NAVADO Project was followed by the Kroonvlag Project (1967-1980),
again with considerable financial aid by ZWO. This project aimed to carry out
geophysical measurements aboard freighters of the KNSM (Royal Netherlands
Steamboat Company) and the SMS (Suriname Shipping Company). The name
Kroonvlag (Crown-Flag) was derived from the Company's flag to which these
ships belonged. A group of marine geophysicists of the Vening Meinesz Laboratory
crossed the North Atlantic Ocean more than 40 times and made a dense
network of geophysical measurements over the Atlantic between 6°N. and 37°
N. latitude. During the crossings the bathymetry, the structure of the ocean
floor, and also the strength of the geomagnetic field were determined. The result
of the magnetic measurements can be found in a publication by Collette et ...
al. (1974). The following scientists cooperated in this research: K. W . Rutten,
J.A. Schouten, A.P. Slootweg, W. Twigt and J. Verhoef. One of the results of
the Kroonvlag Project was a detailed survey of the Mid-Atlantic Ridge, especially
of the fracture zones and the central rift zone. Collette (1974) explained
the fractures in ocean ridges as shrinking cracks in the cooling oceanic crust.
1.8.4. Atlantic Ocean: Vaarplan Projects
In 1977 a new period for oceanography in the Netherlands commenced with
the commissioning of the research vessel H.NI.M . S. Tydeman. It was built to
replace the hydrographic vessels H.Nl.M.S. Snellius and Luymes (see Chapter
11, section 7.5).
A scientific program, Vaarplan (Sailing Scheme) 1974-1978, followed by Vaarplan
1978-1982, was developed by the Netherlands Council of Oceanic Research
34

W
0\
Figure 18. The oceanographic research vessel H .Nl.M .S. Tydeman (photo courtesy of
the Audio-Visual Service of the Royal Netherlands Navy).

of the Royal Netherlands Academy of Arts and Sciences to serve the ocean disciplines
in the fields of physical oceanography. meteorology. chemical oceanography.
marine biology. marine geology and geochemistry. and marine geophysics.
The Vening Meinesz Laboratory was charged with the marine geophysical program.
Funds became available for computer systems for on-board data handling.
satellite navigation systems. renovation of the gravimeter and the magnetometers.
and for a powerful compressor and airguns.
Apart from H. Nl.M. S. Tydeman the Marine Geophysics Group used chartered
cargo vessels. In 1975 research was carried out on the Mid-Atlantic Ridge by
means of the M.S. Aegeon Express. and in 1977. 1978 and 1979 with the M.S.
Tyro. again on the Mid-Atlantic Ridge and also in the basins east of the Ridge.
The first results of the geophysical measurements on board of the H.Nl.M.S.
Tydeman were embodied in a publication by Twigt. Collette and Slootweg (1979).
1.8.5. Atlantic Ocean: other subjects
J. A. Schouten developed in his thesis (1970) a fundamental method for analyzing
geomagnetic anomalies over ocean ridges. This method was applied to
the geomagnetic anomalies in the Atlantic Ocean and in the Bay of Biscay (Schouten
et al.. 1971). Rutten analyzed the anomalies off Iceland in his thesis (1975).
W. J. M. van der Linden (1975) presented an interpretation of magnetic anomaly
and basement trends in the Atlantic • concerning sea floor spreading in the Labrador
Sea. He also discussed morphology. magnetic and seismic characteristics
indicating that the area west of Iberia and Morocco is a deformed passive continental
margin (Van der Linden. 1979). He proposed (1980) that the eastern
Walvis Ridge is a continental fragment that was originally positioned marginal
to Africa.
It is the intention of the Marine Geophysics Group to study in thè near future.
among other subjects. sea floor spreading by investigating geomagnetic
anomalies and gravity on the Mid-Atlantic Ridge. This may result in more information
about movements of the continents on both sides of the Atlantic. In
1979 a study of the problem of young volcanism at the bottom of the Atlantic
Ocean was started. Measurements above the submarine Atlantic-Meteor mountains
were carried out.
I. 9. PALAEOMAGNETIC RESEARCH
Interest of Netherlands geologists and geophysicists in the magnetic properties
of rocks (and especially in palaeomagnetism. which is the fossil remanent
magnetization) was aroused around 1950. when a student of geology from
Utrecht University. J. Hospers • discovered Tertiary basalt flows in Iceland.
which showed a natural remanent magnetization whose direction was opposite
to the present direction of the earth '5 magnetic field. Hospers had collected
his basalt samples at the request of W. Nieuwenkamp (professor of petrology
at Utrecht) who assumed that the phenomenon of reversed magnetization of
basalt. which had been discovered by J. Brunhes in 1906 in France. perhaps
would appear also in basalts from Iceland. Since at that time a suitable apparatus
for measuring rock magnetism was not yet available in the Netherlands •
Hospers studied his rocks in the Geological Laboratory of Cambridge University.
where he finished his doctor's thesis. His investigation was published in
the Proceedings of the Royal Netherlands Academy of Arts and Sciences (Hospers.
1953 and 1954). Hospers concluded that the geomagnetic field must have
changed its polarity repeatedly during Tertiary times. that is to say that the
37

geomagnetic poles have changed several times. Moreover • he found that at least
during the Miocene the mean geomagnetic ,pole practica11y coincided with the
geographic pole.
M . G . R utten, professor of geology at Utrecht, recognized an agreement between
the result of investigations by Hospers on the polarity of lavas on Iceland
and those in the Plateau Central in France, found by A. Roche . For example,
both investigators dated the latest period of reversed polarity at the beginning
of Pleistocene. M. G. Rutten and J. C. den Boer (1954) realized that
palaeomagnetism can be used for correlating lava flows over large distances.
The outcome of Hospers' research was that, at the instigation of M. G. Rutten,
a beginning was made in 1955 into the investigation of the magnetism of rocks.
This took place under the guidance of Veldkamp • professor of geophysics at
Utrecht from 1955 ti11 1974. Because Veldkamp was at the same time director of
the geophysical dep art ment of the KNMI (from 1945 till 1972) this research was
conducted for the first years in the seismograph pavilion of the KNMI. The
instruments and measuring methods we re developed by J. A. As (KNMI) and
the first results were found there.
This was the beginning of a very fruitful development in cooperation bet ween
geophysicists and geologists at Utrecht University. On the one hand the geologist
could provide rock samples whose orientation was observed and measured
in situ, on the other hand the geophysicist could measure the direction and
the intensity of the magnetic components in the rock sample. This made possible
in favourable cases determination of the direction of the local geomagnetic
field at the time of the formation of the rock. From this direction conclusions
could be drawn about the former positions of continents or of parts thereof.
This cooperation bet ween geophysicists and geologists has resulted in a series
of publications and theses produced at Utrecht University. In total no less
than 18 dissèrtations and a number of papers were produced under the supervision
of M.G. Rutten, R.W. van Bemmelen, J. Veldkamp and J.D.A. Zijderveld.
The contents of these publications were to a considerable degree based on the
study of palaeomagnetism .
J.A. As (1960) developed the instruments necessary for measuring the magnetism
of rocks. These instruments (astatic magnetometers and A. C. -demagnetization
coils) were constructed at the KNMI and set up in the seismograph
pavilion. As and Zijderveld (1958) designed methods for analyzing the magnetism
of rocks. by means of heating as we11 as by demagnetization step by step
in alternating magnetic fields. These methods made it possible to separate the
fossil magnetism in a rock sample from recent magnetizations (see also: Zijderveld
, 1967. and R. O. van Everdingen • 1960).
Whereas origina11y demagnetization was applied only to test the stability of
the remanent magnetization of rocks. the step-wise demagnetization developed
by As and Zijderveld became important for separating vectorially the magnetizations
present in the rock samples. In many cases the direction of the original
magnetization could be derived with reasonable accuracy. This allowed
calculation of the position of the geomagnetic po Ie at the time of the formation
of the rock , and from this the geographic latitude of the country where the
rock sample was taken. In favourable cases even the intensity of the fossil
geomagnetic force could be found.
In 1963 the magnetometers and demagnetization instruments were transferred
to the former Fort Hoofddijk , which was rebuilt by Utrecht University especia11y
for magnetic measurements. The research in rock magnetism has continued there
under the leaders hip of Zijderveld . The Palaeomagnetic Laboratory contains
now, in addition to the astatic magnetometers and the demagnetization apparatus,
a spinner magnetometer, a cryogenic magnetometer , a magnetometer for
38

Figure 19. The Palaeomagnetic Laboratory of the State University at Utrecht. formerly
Fort Hoofddijk (Photo e.G. Langereis) .

low and high temperatures, an electromagnet for investigating the magnetic
minerals in a rock sample, and also a sensitive measuring bridge for measuring
the magnetic susceptibility of rocks. J. A. As developed a method for determining
the susceptibility tensor by means of the astatic magnetometer (As, 1967).
1.9.1. Palaeomagnetism at the State University of Utrecht
Below a summary is given of the palaeomagnetic research that was accomplished
at the Utrecht University.
a. Stabie Europe. Palaeomagnetic research was in the beginning focused on
some regions in the stabie non-alpine part of Europe, where Rutten took the
Figure 20. Geomagnetic declination (arrows) and inclination (numbers) in Europe
during the Permian. The earth 's magnetic field had a southward direction , opposite
to the present direction . The dotted line denotes the border of Stabie Europe. North
of this line the declinations and inclinations of Permian rocks in various countries
are reasonably consistent with each other. However. the declinations in Spain and
Portugal deviate a g>:'eat deal from those in Stabie Europe. but after a clockwise rotation
of 35° the fossil geomagnetic directions in Spain and Portugal agree weU with
those in Stabie Europe. This points to a counter-clockwise rotation of the Iberian
Peninsuia since Permian times (Van der Voo and Zijderveld • 1969; see also: Zijderveld
and Van der Voo. 1973).
40

k. Mediterranean. Zijderveld continued with other research workers investigations
in the Mediterranean region, in order to study tectonic movements in
the Tethys zone. An extensive report has been written by Van der Voo and
Zijderveld (1969). In the western part of the Mediterranean the deviating directions
of the remanent magnetization of rocks could be explained either by
an eastward displacement of Africa with respect to Europe (with a rotation of
Spain, Sardinia and Corsica) or by a connection to the African block. A coher-
140 MA 95 MA
t25MA 80 MA
110 MA 65 MA
Figure 22. Mesozoic reconstruction of the western part of the Mcditerranean (Van den
Berg. 1979). The palaeomagnetism of rocks proves· that the Mediterranean region
underwent considerable change as a consequence of the shifting of Southern Europe
in relation to Africa. During the Late Cretaceous (between 95 and 65 million years
ago. see right side of diagram) the Iberian Peninsuia moved so that the Bay of Biscay
opened up. Italy was joined to the African continent until the Early Tertiary (65
million years ago, bottom right diagram). but af ter the Eocene (50 million years ago)
Italy rotated away from Africa.
43

ence between the Southern Alps and Africa was presumed by Zijderveld et al.
(1970) in a paper on shear in the Tethy.s zone and the Permian palaeomagnetism
in the Southern Alps. At that time no choice could be made. In a more complete
review Zijderveld and Van der Voo (1973) concluded that the Iberian Peninsuia ,
Sardinia, Corsica and Northern Italy had rotated as a result of shifting of Europe
relative to Africa. In the Eastern Mediterranean the magnetic data proved
that Turkey belonged to the African block during the Cretaceous. but separated
from Africa after that time.
Further research by J. van den Berg, C. T. Klootwijk and A. A. H. Wonders
(1978), and also by Van den Berg and Wonders (1976) led to the conclusion
Figure 23. Path of the magnetic North Pole during a reversal in polarity of the earth's
magnetic field (Dijksman , 1977). The Pole moved from the southern hemisphere (positions
10 to 15) to northern regions • while the dipole moment of the geomagnetic field
became abnormally smalI. Af ter arrival in the northern hemisphere (positions 17 to
20) the intensity of the earth's magnetic field increased gradually to the normal value.
The total reversal of polarity took about 15,000 years. During the Tertiary about 100
reversals in polarity of the earth's magnetic field took place.
44

1. Other studies. The palaeomagnetic research in the Mediterranean region
gave rise to some special doctor 's theses. A. A. Dijksman investigated changes
in the geomagnetic polarity in a column of Miocene sediments in Spain (1977) .
He was able to describe the behaviour of the geomagnetic field during some reversals
. The investigation of sediments in Southern France by C. van den Ende
(1977) gave information on the secular variation of the earth's magnetic field
during the Permian. He also studied the magnetic susceptibility of rocks in order
to find a possible relation between the anisotropy of susceptibility and natural
remanent magnetization. FinaIly, the thesis written by P. H. M. Dankers
(1978) must be mentioned; it deals with the relation between the magnetic properties
and the grain size of magnetic minerals and the influence of temperature
on this relationship .
1.9.2. Palaeomagnetism at the Municipal University of Amsterdam
Under the leadership of J. Hospers , professor in Amsterdam from 1965 to
1975, various palaeomagnetic studies were initiated at the Municipal University.
J. Hospers and S.l. van Andel (1967 and 1968) tried to calculate from palaeomagnetic
data the value of the earth's radius in several geological periods. These
data showed that a constant radius could be supposed as weIl as a slow expansion
of the earth or a small contraction . At any rate the break-up of the Pangaea
continents cannot be explained by an expanding earth. This research led to
the thesis of Van Andel (1968). H.M. van Montfrans (1971), who was also at the
Municipal University of Amsterdam, investigated Quaternary sediments from
the North Sea basin to look for a correlation bet ween the stratigraphic levels
and the time scale of the reversals in the earth 's field. It turned out to be
possible to date a number of levels by means of reversals of geomagnetic polarity.
The palaeomagnetic research of Hospers and his co-workers at Amsterdam
ended when in 1975 geophysics in the Netherlands was concentrated at the
State University of Utrecht.
It is expected that the magnetic properties of rocks and especially the study
of palaeomagnetism under the leadership of Zijderveld , who was appointed professor
at Utrecht in 1981, will yield important information about the processes
and movements in the crust of the earth.
REFERENCES TO CHAPTER I
Andel, S.1. van (1968) - A test of earth expansion hypotheses by means of
paleomagnetic data. Proefschrift, Amsterdam.
Anonymous (1967) - NAVADO 111. Bathymetric, magnetic and gravity investigations,
1964-1965. Hydrographic Newsletter, Spec. Publ. Nr. 3, parts 1,
2 and 3, 1967.
As, J.A. and J.D.A . Zijderveld (1958) - Magnetic cleaning in paleomagnetic
research . Geophys. Journ. Roy. Astr. Soc., 1,308-319.
As, J. A. (1960) - Instruments and measuring methods in paleomagnetic research.
Meded. en Verh. K.N.M.I., Nr. 78.
As, J.A. (1967a) - Past, present and future changes in the earth's magnetic
field. Magnetism and the Cosmos , 29-44, 1967, Oliver and Boyd, Edinburgh.
As, J.A. (1967b) - Measurement of the anisotropy of the susceptibility. In:
Methods in Paleomagnetic Research, 362-367, Elsevier, Amsterdam.
46

As, J.A. (1973) - The compensation method for measuring the components of
the earth's magnetic field. Zeitschr. für Geophysik, 39, 303-311, 1973.
As, J .A. (1975) - World-wide beits in the earth's magnetic field . Progress in
geodynamics, Proc. nat. symp. on geodynamics held in Amsterdam, North
Holland Publ. Cy . Amsterdam, 1975.
Bemmelen , W. van (1892) - Historisch overzicht van de aardmagnetische waarnemingen
in Nederland. Jaarboek K. N .M . I., 1892, De Bilt.
Bemmelen , W. van (1893) - De isogenen der 16e en 17e eeuw. Proefschrift,
Leiden.
Bemmelen, W. van (1897) - Werte der erdmagnetischen Deklination 1500-1700,
und ihrer Säcular-Variation 1500-1850. Kon. Ned. Akad. Wet., Amsterdam.
Bemmelen, W. van (1909) - Magnetic Survey of the Dutch East-Indies made in
the years 1903-1907. Waarn. Kon. Magn. Met. Obs. Batavia, Vol. 30.
Bemmelen, W. van (1920) - De seculaire veranderingen der aardmagnetische
Declinatie, Inclinatie en Horizontale Intensiteit in de westelijke helft van
den Oost-Indischen Archipel, 1905-1916/18. Nat. Tijdschr. Ned. Indië,
79, 202-204, 1920.
Berg, J . van den, and A .A.H. Wonders (1976) - Paleomagnetic evidence of large
fault displacements around the Po-basin . Tectonophysics, 33, 301-320.
Berg, J. van den, C.T. Klootwijk and A.A.H. Wonders (1978) - Late Mesozoic
and Cenozoic movements of the Italian Peninsuia . Further paleomagnetic
data from the Umbrian sequence. Geol. Soc. Amer. Bull., 89,133-150.
Berg, J. van den (1979) - Paleomagnetism and the changing configuration of
the Western Mediterranean area in the Mesozoic and Cenozoic eras. Proefschrift,
Utrecht .
Boeckel, J. J.G.M . van (1968) - Gravitational and geomagnetic investigations
in Surinam and their structural implications. Proefschrift, Amsterdam.
Also in : Mededelingen Geol. Mijnb. Dienst, 1968, Paramaribo, Suriname.
Boer, J. de (1963) - The geology of the Vicentinian Alps (NE-Italy). Proefschrift,
Utrecht.
Boer, J.C. den (1957) - Etude géologique et paléomagnétique des montagnes
d u Coiron (Ardèche, France). Proefschrift, Utrecht.
Bremmer , H. (1949) - Terrestrial Radio Waves: Theory of Propagation . Elsevier,
Amsterdam.
Bremmer , H. (1958) - Propagation of electromagnetic waves. Encyclopaedia of
Physics, 16, 423-639. Springer, New York.
Bruins , E . M. (1938) - Cosmische stralen in het aardmagnetisch veld . Dissertatie,
Amsterdam.
Clay , J. (1932) The Earthmagnetic effect and the Corpuscular Nature of (Cosmic)
Ultra-radiation. Proc. Kon. Ned. Akad. Wet. , Amsterdam, 35, 1282.
Clay, J. (1948) - Kosmische stralen. Servire, Den Haag.
Collette , B.J., R.A. Lagaay, A.P . van Lennep, J . A. Schouten and R.D. Schuiling
(1968) - Some heat-flow measurements in the North AUantic Ocean.
Proc. Kon . Ned. Akad. Wet., Series B, 71, 203-208, 1968.
47

Collette, B.J., K.W. Rutten, J.A. Schouten and A.P. Slootweg (1974) - Continuous
seismic and magnetic profiles over the Mid Atlantic Ridge between
12°N. and 18°N. Marine Geophys. Res., 2,133-141,1974.
Collette, B.J. (1974) - Thermal contract ion joints in a spreading sea-floor as
origin of fracture zones. Nature, 251, 299-300,1974.
Dankers , P. H.M. (1978) - Magnetic properties of dispersed natural iron-oxides
of known grain-size. Proefschrift, Utrecht.
Dietzel, G. F. L. (1960) - Geology and Permian Paleomagnetism of the Merano
region (Province of Bolzano, N.-Italy). Proefschrift, Utrecht.
Dijksman, A.A. (1977) - Geomagnetic reversals as recorded in the Miocene red
beds of the Calatayud-Teruel basin (Central Spain) . Proefschrift, Utrecht.
Dongen, P.G. van (1967) - The rotation of Spain: paleomagnetic evidence from
the Eastern Pyrenees. Paleogeogr., Paleoclim., Paleooecol., 3, 417-432,1967.
Dongen, P.G. van, R. van der Voo and Th. Raven (1967) - Paleomagnetism and
the Alpine tectonics of Eurasia (part 3). Paleomagnetic research in the
Central Lebanon mountains and in the Tartous area (Syria). Tectonophysics,
4, 35-53,1967.
Elias, G.J. (1923) - Over de voortplanting van electromagnetische trillingen.
Tijdschrift Ned. Radio Gen., 2, 1-21.
Ende, C. van den (1977) - Paleomagnetism of Permian red beds of the Dame de
Barrot (Southern France). Proefschrift, Utrecht.
Everdingen , R.O. van (1960) - Paleomagnetic analysis of Permian extrusives
in the Oslo region, Norway. Proefschrift, Utrecht.
Gregor, C.B. and J.D.A. Zijderveld (1964) - Paleomagnetism and the Alpine
tectonics of Eurasia, part I. The magnetism of some Permian red sandstones
from northwestern Turkey. Tectonophysics, 1, 289-306, 1964.
Groenewold, H . J. (1948) - De betekenis van de toestand der ionosfeer voor
radioverbindingen op lange afstand. Tijdschr. van het Ned. Radiogenootschap,
13, 103-139.
Groenewold, H. J. (1949) - Ionosfeeronderzoek . Ned. Tijdschrift voor Natuurkunde,
15, 157-168.
Groenewold, H.J. (1950) - Triple splitting in a regular layer. Int. Council of
Scient. Unions , Mixed Comm. on lonosphere, Proc. Second Meeting, Brussels,
201-205.
Guicherit , R. (1964) - Gravity tectonics, gravity field, and paleomagnetism in
NE-Italy. Proefschrift, Utrecht.
Hartmann, Ph.C.P. (1945) - Aardmagnetische anomalieën in Nederland. Proefschrift,
Utrecht.
Hilten, D. van (1960) - Geology and Permian Paleomagnetism of the Val-di-Non
area (W. Dolomites, N. Italy). Proefschrift, Utrecht.
Hilton, D. van (1962) - Presentation of paleomagnetic data, polar wandering
and continental drift. Amer. Journ. Sc., Vol. 260, 401-426, 1962.
Hilten, D. van (1964) - Evaluation of some geotectonic hypotheses by paleomagnetism.
Tectonophysics, 1, 3-71, 1964.
48

Hilten, D. van, and J.D.A. Zijderveld (1966) - The magnetism of the Permian
porphyries near Lugano (Northern Italy /Switzerland). Tectonophysics, 3,
429-449, 1966.
Hilten, D. van (1968) - Global expansion and paleomagnetic data. Tectonophysics,
5,191-210, 1968.
Hooykaas, R. (1976) - Geschiedenis der natuurwetenschappen. Utrecht, 1976.
Hooykaas, R. (1980) - Science in Manueline style. Academia Internacional da
Cultura Portuguesa, Coimbra.
Hospers , J. (1953 and 1954) - Reversals of the main geomagnetic field .. I, 11,
111. Proc. Kon. Ned. Akad. Wet., 56, 467-476; 56, 477-491; 57,112-121.
Hospers , J. and S. I. van Andel (1967) - Paleomagnetism and the hypothesis of
an expanding earth. Tectonophysics, 5, 5-24,1967.
Hospers , J. and S. I. van Andel (1968) - Paleomagnetism and the hypothesis of
an expanding earth: a new calculation method and its results. Tectonophysics,
5, 273-285, 1968.
I.A.G.A. (1949-1968) - Bulletin on Geomagnetic Indices, Rapid Variations,
Magnetic Storms. K. N .M. I. , De Bilt.
I.A.G.A. (1969-now) - Bulletin on Geomagnetic Indices, Rapid Variations,
Magnetic Storm. K.N.M.I., De Bilt.
Jongen, H. F. (1952) - Problemen omtrent de oorsprong van de kosmische straling.
Dissertatie, Amsterdam.
Kelder, H. (1975) - Een eenvoudig model voor de berekening van de verandering
in de ionendichtheid van de E-Iaag veroorzaakt door een inwendige
zwaartekracht golf. K.N.M.1. Wetensch. Rapport 75-12,1975.
Kelder, H. (1976) - Reflection of the semi-diurnal tide in the thermosphere.
E.O.S. Transactions A.G.U., 57, 668-669,1976.
Klootwijk , C. T. (1974) - Paleomagnetic results on a dolerite sill of Deccan Trap
age in the Sonhat coal basin, India. Tectonophysics, 22, 335-353,1974.
Klootwijk , C . T. (1974a) - Paleomagnetism of Indian rocks and implications for
the drift of the Indian part of Gondwanaland. Proefschrift, Utrecht.
Klootwijk, C. T. (1975) - Paleomagnetism of Upper Permian redbeds in the Wardha
Valley, Central India. Tectonophysics, 23,115-137,1975.
K. M.M.O. (1871) - Observations made at the Magnetic and Meteorological Observatory
at Batavia, Vol. 1 (1866-1870).
K.N.M.1. (1894) - Meteorologisch Jaarboek 1894. K.N.M.I., De Bilt.
K.N.M.1. (1903-heden) - Jaarboeken B - Aardmagnetisme, 1903-heden. K.N.
M. 1., De Bilt.
K. N .M. I. (1949-heden) - Monthly Bulletin on ionospheric, geomagnetic, etc.
data.
K.N.M.1. (1954) - Gedenkboek van het Koninklijk Nederlands Meteorologisch
Instituut, 1854 -1954. Staatsdrukkerij, 's-Gravenhage.
Kruseman, G.P. (1961) - Etude paléomagnétique et sédimentologique du Bassin
Permien de Lodève (Hérault, France). Proefschrift, Utrecht.
49

Lagaay, R .A. (1968) - Geophysical investigations of the Netherlands Leeward
Antilles . Proefschrift. Utrecht.
Linden, W.J.M. van der (1975) - Mesozoic and Cainozoic opening of the Labrador
Sea, the North Atlantic and the Bay of Biscay. Nature, 253, 320-324.
Linden, W.J.M. van der (1979) - The Atlantic margin of Iberia and Morocco, a
re-interpretation. Tectonophysics, 59,185-199.
Linden, W.J.M. van der (1980) - Walvis Ridge, a piece of Africa? Geology, 8,
417-421.
Lith, P.A. van der, en J.F. Snelleman, red. (1919) - Encyclopaedie van Nederlands
Indië, deel 3, 41-50.
Montfrans, H.M. van (1971) - Paleomagnetic dating in the North Sea Basin.
Proefschrift, Amsterdam.
Mulder, F.G . (1970) - Paleomagnetic research in some parts of Central and
Southern Sweden, Sver. Geol. Unders. , Ser. C 653, 1970. Proefschrift,
Utrecht.
Pannekoek , A. (1926) - lonisation Equilibrium in SteUar Atmospheres and in
the Earth's Atmosphere. Proc. Roy. Acad. Amsterdam, 29,1165-1171.
Pol, Balth. van der (1920) - De invloed van een geïoniseerd gas op het voortschrijden
van electromagnetische golven, enz. Proefschrift, Utrecht.
Poorter, R.P.E. (1976) - Paleomagnetism of Precambrian rocks from Norway
and Sweden. Proefschrift, Utrecht.
Prins, J .A. (1933) - Latitude effect of Cosmic Radiation. Nature, 132, 781.
Rijckevorsel, E. van (1879) - Magnetische opneming van den Indischen Archipel,
1874-1877. Kon. Ned. Akad. van Wet., Amsterdam.
Rijckevorsel, E. van, and E. Engelenburg (1890) - Magnetic Survey of the eastern
part of Brasil 1880-1885. Kon. Ned. Akad. van Wet., Amsterdam.
Rijckevorsel, E. van (1895) - A magnetic survey of the Netherlands for the
epoch January 1, 1891. Nieuwe Verhandelingen van het Bataafse Genootschap
der Proefondervindelijke Wijsbegeerte, Rotterdam.
Rijckevorsel, E. van, en W. van Bemmelen (1899) - Magnetische Beobachtungen
in der Schweiz. K.N.M.I., De Bilt.
Rutten, K.W. (1975) - Two-dimensionality of magnetic anomalies over Iceland
and Reykjanes Ridge. Marine Geoph. Res., 2, 243-263,1975. Proefschrift,
Utrecht.
Rutten, M.G. and J.C. den Boer (1954) - Inversion de l'aimantation dans les
basaltes d u Co iron (Ardèche). C. R. de la Société Géologiq ue de France,
no. 5,106-107,1954.
Sabben, D. van (1961) - lonospheric current systems of ten l.G. Y .-solar flare
effects. Journ. Atm. Terr. Phys. 22, 32-42,1961.
Sabben, D. van (1962) - lonospheric current systems caused by non-periodic
winds. Journ. Atm. Terr. Phys. 24, 959-974,1962.
Sabben, D. van (1964) - North-South asymmetry of Sq. Journ. Atm. Terr.
Phys., 26, 1187-1195.
50

Sabben, D. van (1966) - Magnetospheric currents, associated with the N-S
asymmetry of Sq. Journ. A tm. Terr. Phys., 28, 965 - 981. See also: Errata­
Journ. Atm. Terr. Phys., 30, 327-329,1968.
Sabben, D. van (1968) - Solar nare effects and simultaneous magnetic daily
variations, 1959-1961. Journ. Atm. Terr. Phys., 30, 1641-1648, 1968.
Sabben, D. van (1969) - The computation of magnetospheric currents caused
by dynamo action in the ionosphere. Journ. Atm. Terr. Phys., 31, 469-
474, 1969.
Sabben, D. van (1970) - Solstitia I Sq -currents through the magnetosphere.
Journ. Atm. Terr. Phys., 32,1331-1336,1970.
Scholte, J.G.J. and -J. Veldkamp (1955) - Geomagnetic and Geoelectric variations.
Journ. Atm. Terr. Phys., 6, 33-45,1955.
Scholte, J.G.J. (1960) - On the theory of giant pulsations. Journ. Atm. Terr.
Phys., 17, 325-336, 1960.
Schouten, J . A. (1970) - A fundamental analysis of magnetic anomalies over
ocean ridges. Marine Geophys. Res., 1, 111-144, 1971. Proefschrift,
Utrecht, 1970.
Schouten, J.A., B.J. Collette, K.W. Rutten (1971) - Magnetic anomaly symmetry
in the Bay of Biscay. Histoire Structurale du Golfe de Gascogne , VI. 13,
Paris, 1971.
Schwarz, E.J. (1963) - A paleomagnetic investigation of Permo-Triassic redbeds
and andesites from the Spanish Pyrenees. Journ. Geophys. Res. 68,
3265-3271, 1963.
Twigt, W., B.J. Collette and A.P. Slootweg (1979) - Topography and magnetic
analysis of an area southeast of the Azores. Marine Geophys. Res., 4,
91-104, 1979.
Veldkamp , J. (1951) - The geomagnetic field of the Netherlands , reduced to
1945,0. Mededelingen en Verhandelingen K.N.M.I., no. 134.
Veldkamp , J. and J.G.J. Scholte (1954) - Some remarks on the Equatorial
Electrojet, as revealed by the analysis of solar flare effects . Indian Journ.
of Meteor. and Geophysics, 5, 203-212,1954.
Veldkamp, J. and J . G.J. Scholte (1954a) - Magnetische dubbele breking in de
ionosfeer. Gedenkboek K.N.M.I., 430-442, 1954.
Veldkamp, J. and D. van Sabben (1960) - On the current system of solar flare
effects. Symposium on rapid magnetic variations, I.A.G.A., Utrecht, 1959.
Journ. Atm. Terr. Phys., 18, 192-202, 1960.
Veldkamp, J. (1960) - A giant geomagnetic pulsation. Journ. Atm. Terr. Physics,
17, 320-324,1960.
Veld kamp , J. and H.J.A. Vesseur (1967) - Geomagnetic anomalies in the western
part of the continental shelf of Surinam. Hydrographic Newsletter,
Spec. Publ., 5, 1967.
Veld kamp , J. and H.J.A. Vesseur (1971) - Geomagnetic anomalies in the continental
shelf of Surinam. Hydrographic Newsletter, Spec. Publ. 6,1971.
Veld kamp , J., F.G. Mulder and J.D.A. Zijderveld (1971) - Paleomagnetism of
Suriname dolerites. Phys. Earth and Planet. Interiors, 4, 370-380, 1971.
51

Veldkamp, J. (1974) - Geofysica. Aula Paperback 20, Het Spectrum, Utrecht.
Vesseur, H.J.A. (1970) - A correlation apparatus for the measurement of the
drift in the ionosphere by the spaced receiver method. Journ. A tm. Terr.
Physics, 32, 829-835,1970.
Vesseur, H.J.A. (1972) - Results of E-Iayer drift measurements at De Bilt.
Phil. Trans. Royal Soc. London, A 271, 485-497,1972.
Vesseur, H.J.A. (1974) - Radioverbindingen via de ionosfeer. Nautisch Technisch
Tijdschrift "De Zee", juni, 1974.
Vesseur, H.J.A. (1977) - Ionosfeeronderzoek op het K.N.M. I. Nederl. Tijdschrift
voor Natuurkunde, A 43,128-134.1977.
Visser, S. W. (1925) - Isomagnetics for the Netherlands East Indian Archipelago,
Epoch 1925,0. Verh. Kon. Magn. Obs. te Batavia, Nr. 13, 1925.
Voo, R. van der (1968) - Paleomagnetism and the Alpine tectonics of Eurasia,
part IV. Jurassic , Cretaceous and Eocene po Ie positions from NE Turkey.
Tectonophysics, 6, 251-269, 1968.
Voo, R. van der, and J.D.A. Zijderveld (1969) - Paleomagnetism in the Western
Mediterranean area. Verh. Kon. Ned. Geol. Mijnb. Gen., Vol. XXVI, 121-138,
1969.
Voo, R. van der (1969) - Paleomagnetic evidence for the rotation of the Iberian
Peninsuia . Proefschrift, Utrecht.
Voo, R. van der, and C. T . Klootwijk (1972) - Paleomagnetic reconnaissance
study of the Flamanville granite, with special reference to the anisotropy
of its susceptibility. Geologie en Mijnbouw 51, 609-617,1972.
Voo, R. van der, and A. Boessenkooi (1973) - Permian paleomagnetic result
from the Western Pyrenees delineating the Plate Boundary bet ween the
Iberian Peninsuia and Stabie Europe. Journ. Geophys. Res., 78, 5118-
5127, 1973.
Wensink, H. (1964a) - Paleomagnetic stratigraphy of younger basalts and intercalated
Plio-Pleistocene tillites in Iceland. Geol. Rundscha u, 54, 364-
385, 1964.
Wensink, H. (1964b) - Secular variation of earth's magnetism in Plio-Pleistocene
basalts of eastern Iceland. Geol. en Mijnb. , 43. 403-413,1964.
Wensink, H. and C. T . Klootwijk (1968) - The paleomagnetism of the Talchir
series of the Lower Gondwana system, Central India. Earth and Plan. Sc.
Lett., 4, 191-196.
Wensink, H. and C. T . Klootwijk (1971) - Paleomagnetism of the Deccan Traps
in the Western Ghats near Poona, India. Tectonophysics, 11, 175-190, 1971.
Zijderveld, J.D.A. (1967) - AC demagnetisation of rocks: analysis of results.
In: Methods in Paleomagnetic Research (1967), 254-286, Elsevier, Amsterdam.
Zijderveld, J.D.A. (1967) - The natural remanent magnetization of the Exeter
volcanic traps (Permian, Europe). Tectonophysics, 4,121-153.1967.
Zijderveld , J . D. A. (1968) - Natural remanent magnetization of some intrusive
rocks from the S

Zijderveld, J.D.A. and R. van der Voo (1973) - Paleomagnetism in the Mediterranean
Area. In: Implications of Continental Drift to the Earth Sciences,
Vol. 1, 133-161, New York, Academie Press, 1973.
Zijderveld, J.D.A. (1975) - Paleomagnetism of the Esterel rocks. Proefschrift,
Utrecht.
Zijderveld, J .D.A., G.J.A. Hazeu, M. Nardin and R. van der Voo (1970) -
Shear in the Tethys and the Permian paleomagnetism in the Southern Alps,
including new results . Tectonophysics, 10, 639-661.
53

Figure 25. Bosch horizontal seismographs . The seismometers are at the left. One of
the drums holding the recording paper on the right. in front of G. van Dijk. first
director of the Geomagnetism and Seismology Division of the KNMI . The horizontal
component of ground motion is magnified by a factor of 20 by these seismographs .
(Photo Haagsch Illustratie- en Persbureau . Amsterdam.)

CHAPTER 11
Seismological Research
11.1. SEISMOLOGICAL INSTRUMENTATION
Although the Netherlands belong to the countries with a very low seismicity,
seismographs were installed in the cellar of the KNMI (Royal Netherlands
Meteorological Institute) at De Bilt af ter the establishment (in 1854) of the Institute
(see: Gedenkboek, 1954). Interest in seismology was aroused by the
scientific successes of German geophysicists in the interpretation of earthquake
records. Moreover the daily care of the instruments and collecting of recordings
of ground vibrations fitted quite weil into the regular working method of
the Meteorological Institute, namely the collection of meteorological data ona
continuous basis.
The first seismographs that were operated at the KNMI (in 1904) we re two
light pendulums af ter Von Rebeur Paschwitz. Their magnification was so small
however that the records were only seldom usabie. In 1908 instruments were
bought which produced a higher magnification of ground movements : two horizontal
Bosch pendulums and an astatic Wiechert seismograph. These seismographs
are now among the museum pieces, which are still successfully demonstrated
to visitors.
In 1912 two horizontal Galitzin seismographs with galvanometric recording
were purchased. A vertical seismograph was installed in 1922. The purchase
of this instrument was not without difficulties. The instrument maker, who
used to construct seismographs for Prince Galitzin, had emigrated from Petersburg
to Dorpat (Estland) because of the revolution , and it took much time and
effort to discover his address. The three Galitzin seismographs still make up a
set of valuable instruments, especially suited for recording earthquakes at great
distances, because of their large eigenperiods.
A Grenet seismograph was purchased in 1949 for recording vibrations with
shorter periods. Because of vibrations due to traffic, it turned out to be impossible
to set up this very sensitive seismograph in the KNMI. The geomagnetic
observatory at Witteveen proved to be a much better place, although not
yet ideal. The Grenet seismograph, because of its high magnification at a period
of about one second, turned out to be especially suitable for recording seismic
waves that have crossed the earth 's core.
A further enlargement of the collection of seismographs came in 1966, when
a set of Press-Ewing seismographs was installed in the seismograph building
at De Bilt. These instruments have a much broader spectrum of magnification
than the Galitzin seismographs; they are even able to record the very long
55

Figure 26. Press-Ewing seismometers. At the left and middle the seismometers for
horizontal movements , at the right the seismometer for vertieal ground movements .
Maximum magnifieation about 1000. Recording system not shown.

11.2.1. Work of J.G.J. Sc holte
J.G.J. Scholte, who worked at the KNMI as a seismologist from 1950 to 1970
and who was at the same time professor of general geophysics at Utrecht University
from 1957 to 1970, made a number of contributions to theoretical seismology.
A very important one deals with the properties of seismie waves in a
spherical earth (Scho/te, 1956). Radiating from a point souree as a model of an
earthquake, the waves propagate and are reflected from and refracted at the
boundary between the solid mantle and the liquid co re and also are reflected
from the earth 's surface . The refIected and refracted waves appear in the mathematical
treatment as infinite series of spherical waves, which can be transformed
into integrals . The integrals are then evaluated by the saddle-point
method.
Scholte also developed a method for determining the propagation of a wave
of arbitrary shape through an inhomogeneous medium in which both density
and velocity change with depth according to an arbitrary continuous function.
The solution is obtained by . successive approximations (Scholte , 1961). A further
paper deals with the propagation of plane waves travelling in an arbitrary
direction through a medium, the elastic parameters and density of which are a
function of the vertical coordinate (Scholte , 1962).
Scho/te (1958) also wrote a treatise on Rayleigh waves in elastic media. Af ter
an exposition of the classical theory, it was extended to the case of a horizontally
isotropie medium, followed by a discussion of the Rayleigh equation for different
classes of crystals. An extension of the method used enabled Scholte to derive
the Stonely wave equation for the wave travelling along the boundary bet ween
two media.
The thesis of H.J. van Veen on the laser seismometer (1969) was written under
supervision of Scholte , while I. Csikós in his thesis dealt with the theory
of the electromagnetic seismograph (1975a).
11.2.2. Research by N.J. V/aar and co-workers
After Scholte's death in 1970, N.J. Vlaar was appointed his successor at
Utrecht University in 1973. Af ter obtaining hls doctor's degree in 1963, Vlaar
had studied the excitation of a seismie pulse in a semi-infinite medium, as weIl
as in a continuously layered inhomogeneous elastic medium (V/aar, 1964, 1966a,
1966b). He also investigated the propagation of seismic waves in an anisotropic
inhomogeneous earth (V/aar, 1968 and 1969). He introduced a development of
the function of Green (a solution of the wave equation) in eigenfunctions , which
can be interpreted as norm al modes of the earth (Vlaar, 1976).
Meanwhile Vlaar had formed a group at the Vening Meinesz Laboratory to
study theoretical seismology and its applications . Contacts with the American­
Norwegian seismograph array NORSAR (near Hamar) resulted in a number of
scientific papers. D. J. Doornbos and E. S. Huseby (1972) investigated the array
analysis of PKP phases and their precursors. Array analysis of core phases
was the subject of a thesis (Doornbos, 1974a) about the properties and structure
of the earth and about the diffusion and damping of waves that pass through
Figure 27. Top: three-component long-period seismograms of an earthquake in the
North Anatolian fault zone as recorded at De Bilt on 3 September 1968. Bottom: radiation
pattern of compressions and dilatations (shown by the short arrows) caused
by dextral block faulting at the hypocentre (lower right) and the direction of initial
P horizontal motion at De Bilt (upper left) , dilatation to the southeast.
59

It became clear that surface wave analysis is an excellent method for investigating
margins of continental plates (Nolet, Panza and Wortel, 1978). A further
paper on higher mode data in Western Europe and Northern Eurasia was published
by M. Cara, A. Nercessian and G. Nolet (1980).
J. C. Mondt (1977a and 1977b) returned in his thesis (1977b) to the problem
already broached by Scholte , viz. the diffraction of seismic waves in the transition
zone between the earth's mantle and core. Based on theoretical models
of the mantle and core he calculated the wave potentials and from these the
amplitudes of the diffracted waves. The results were worked through further
by Doornbos and Mondt (19798 and 1979b).
Stimulated by the growing number of observations of free vibrations of the
earth, Vlaar (1976) published a paper on the excitation of these vibrations, in
which he ceased using the model of a point source. An earthquake can be caused
by a dislocation (block faulting) but also by a sudden change of volume (implosion
by phase transition) . This gave rise to a further study of gravity effects
of a volume source (Vlaar and Wortel, 1978). Doornbos (1977) wrote an
article on the excitation of normal modes by an implosion . The distribution of
energy among the various higher modes of the free vibrations of the earth
caused by an implosion differs from that caused by block faulting.
After a certain stabilization of the seismological research, the theoretical
geophysics group at the Vening Meinesz Laboratory at Utrecht started studying
tectonophysical problems under Vlaar's leadership . This was induced by
an hypothesis advanced by Vlaar (1975) stating that the increasing gravitational
instability of the ageing and cooling oceanic lithosphere-upper mantle
system should play an important role in plate tectonics. This idea was further
developed in a paper by Vlaar and Wortel (1976) and in M. J. R. Wortel's thesis
(1980). Wortel and Vlaar (1978) and P. England and Wortel (1980) elaborated
on the same theme with applications associated with the South American subduction
zone. The rheological properties and vertical velocity of the sinking
lithosphere are determined by age. If one takes this age dependence into account,
the differences between various zones of subduction can be explained.
The stress fields in the zones of subduction can be calculated. The creation
of tension zones with volcanism then becomes understandable, just as does the
appearance of earthq uakes at other places.
The seismological-geotectonic research in the Vening Meinesz Laboratory is
continuing. In the ne ar future a Netherlands Network of Automatically Recording
Stations (NARS-project) will be set up, with financial aid from the Netherlands
Organization for the Advancement of Pure Research (ZWO) and from the
European Science Foundation (ESF), in order to have available a homogeneous
collection of seismograph data, suitable for the investigation of the higher modes
of surface waves (Vlaar and Nolet, 1979).
II.3. EARTHQUAKE MECHANISMS
Several Netherlands seismologists have shown a special interest in research
into the mechanism responsible for the emission of seismic waves from the focus
of an earthquake. L. P. G. Koning (1941 and 1942) was the first to tackle this
problem. In his thesis he came to the conclusion that the model of an earthq
uake mechanism, in which the first onsets of the P waves are divided - as
compressions and dilatations - into a system of quadrants in the hypocentre,
was suitable for the earthquakes studied by him.
A system of four quadrants of compressional and dilatational waves must appear,
if the earthquake is due to a sudden relative displacement of two blocks
61

along a fault. Block faulting can be expected when the earth's crust or mantle
yields locally to a gradually increasing stress. Indeed, such displacements ,
horizontal or vertical, can sometimes be obèerved at the surface of the earth
af ter a large shallow earthquake. The problem is, however, that the seismic
rays undergo considerable changes of direction in travelling through the interior
of the earth. As a consequence, the boundaries bet ween compressions
and dilatations plotted on the earth 's surface , are deformed into irregularly
bent surfaces , and it is difficult to find them.
11.3. 1. Research by A . R. Ritsema and others
Af ter Koning, research into earthquake mechanisms was continued and extended
by A. R. Ritserna , who worked at the Meteorological and Geophysical
Institute (Lembaga Meteorologi dan Geofisik) of Indonesia at Jakarta from 1952
until1958, and at the KNMI since then. Ritserna introduced an important improvement
into the method of research by bringing the observed compressions and
dilatations back to the vicinity of the hypocentre. This amounts to projecting
the seismograph stations on a small constant-velocity sphere cent red at the
focus of the earthquake. On this sp here the quadrants of compression and dilatation
are separated by great circles , which interseet perpendicularly.
In his thesis (1952) Ritsema introduced a stereographic representation of the
focal sphere , so that the separation of compressions from dilatations (first arrivals
of pressure- and tension-waves) could be constructed easily in case of
a sufficient number of seismograph stations . A further extension of this research
became possible by studying compound patterns of compressions and
dilatations of more earthquakes in a certain region (Ritsema, 1954). He used
for the first time initial arrivals of S waves to supplement the study of P waves
o 10· 2(1' 3(f' 40· 50· 6(f' 70· 8(f' 90· 100· 110· 120· 130· 140· 150· 160· 170· 180·
320· 310· 300' 290' 28(f' 270' 260' 25(f' 240' 23r:t' 220' 210· 200· 190' 180·
Figure 29. Graphs for calculating the angles (on vertieal seale) at which seismie
waves leave the foeus of an earthquake, to emerge at a seismograph station (distanee
between epieentre and station on horizontal seale) . See : Ritsema, 1958. Assumed
depth of foeus 600 km.
62

(Ritsema, 1957). In order to facilitate projection of seismograph observatories
on the focal sphere he calculated standard curves which are useable for all
epicentral distances and possible depths of the hypocentre (Ritsema, 1958).
A theoretical model of an earthquake focus with a finite volume (instead of
a point source) was drafted in cooperation with Scholte (1962a), and the partition
of compressions and dilatations calculated and compared with observations
(Ritsema, 1962). Scholte himself (1962b) also wrote a paper on the problem of
focal mechanisms bf earthquakes. An improvement of Scholte's model was accomplished
by Csik6s (1975b).
11.3.2. Work of J.A. Steketee
At the request of J. Tuzo Wilson, professor of geophysics at the University
of Toronto, J. A. Steketee who had graduated in aerodynamics from the University
of Technology (TH) at Delft, began a study of some geophysical problems
in 1955. Steketee was successively lecturer and assistent professor in
applied mathematics at the University of Toronto from 1950 to 1960; then he
returned to Delft, where he became professor of aerodynamics in 1960.
In his first papers on fractures in the earth's crust (195& and 1958b) Steketee
suggested that Volterra's theory of dislocations might be a proper tooI
for a quantitative description of fracture zones in the crust. The term "elasticity
theory of dislocations" (ETD) was introduced as an appropriate means
to denote a special part of the classical theory of elasticity. Bya careful analy'sis
of the kernels in the representation theorem of Betti-Somigliana, Steketee
identified elastic dislocations as surface distributions of double coup les in the
static case. Elastic dislocations were observed from the 1906 San Francisco earthquake
(largest at faultbreak and decreasing with increasing distance from it).
In the ETD the earth is considered as a semi-infinite elastic medium with a
stress free surface . The displacement field, caused by a stress pattern, is discussed,
and an attempt is made to relate some simple cases in the ETD to certain
geophysical features. Together with two graduate students Steketee applied
ETD to calculations on a model of the 1906 San Francisco earthquake and two
Japanese earthquakes.
In some further papers Steketee (1974, 1975 and 1976) used a time dependent
ETD, which can be applied to geophysics. Prescribing an earthquake mechanism
(e. g. a double coup Ie at a moving focus) one could calculate, at least in principle,
the displacement field and the waves emitted. The result can be compared
with experimental data.
11.3.3. Results of research in earthquake mechanisms
Earthquake mechanisms yield information about stresses in the crust and
mantle in regions where earthquakes occur. Stress fields have become of great
importance in the theory of plate tectonics. The directions of maximum and
minimum stresses in the rocks at the hypocentre of an earthquake, which are
calculated from the partition of compressions and dilatations , can be related
directly to stresses in the plates of the lithosphere. Research into mechanisms
of a number of earthquakes in a seismic region (which mostly coincides with a
border zone between pla.tes) can give indications about recent movements of
the plates.
IJ. 3. 3.1. Southeast Asia and Hindu Kush
After some individual papers by both authors in earlier years, a summarizing
63

of the Anatolian-Aegean block with respect to Eurasia and Africa, and a westeast
extension of the western Mediterranean basin with respect to North Africa
and the Italian Peninsuia . Dextral strike-slip fault movements occur in a zone
extending from the Azores through Africa to North Anatolia. Sinistral fault
movements are observed in the Balkans and the region of the Red Sea.
In combining these phenomena, it appears that the western part of the Mediterranean
shifts to the east, with the Calabrian Arc sliding over the Ionian Sea
in an east-southeast direction. This is the cause of the deep Tyrrhenian subduction
zone, with earthquakes down to 500 km and a compressive stress in the
dip direction of the zone. The eastern part of the Mediterranean moves to the
west, bet ween the North Anatolian zone and the Red Sea Rift. The Aegean Sea
region is a down-rifted subsiding zone, fringed by the subduction zone of the
Hellenic Arc.
The relative movement of the Aegean-Anatolian block with respect to that of
the Ionian Sea is a subduction of the latter in a general SW to NE direction .
Intermediate focus earthquakes occur in the Aegean Sea to a depth of 170 km.
The rare very deep earthquakes under South Spain (at a depth of about 600
km) do not have a generally accepted explanation.
Earthquakes in the Tyrrhenian Sea induced Ritsema (1972 and 1979) to a view
on active and passive subduction. The crust below the Tyrrhenian Sea has been
stretched and oceanized by the eastward drift of the Calabrian Arc. Volcanism
appears bet ween the fragments of the originally continental crust. The Ionian
block is stabie and must probably be considered as a part of Africa. The mechanisms
of earthquakes in the Calabrian zone can best be explained by passive
subduction, that is to say an overthrust of the Tyrrhenian block over the African
plate. The process of subduction in the Tyrrhenian Sea and in the Aegean
Sea can be looked up on as the final phase of the disappearance of the former
Tethys Sea, which was sqeezed bet ween Africa and Eurasia.
Figure 31. The movement of lithospheric plates or blocks in the Mediterranean region.
The eastern part of the Mediterranean Sea moves to the west, and the western
part to the east. The Aegean Sea is a subduction zone (Ritsema, 1969a).
65

II. 4.1. Seismicity of the Mediterranean region
Seismicity in the eastern part of the Mediterranean Sea shows the remarkable
phenomenon of travelling epicentres. Series of earthquakes occur in the eastern
part of the Mediterranean and along the Anatolian-Aegean block (Ritsema, 1975b).
For instance, after astrong earthquake in Anatolia sometimes series of shocks
occur whose epicentres travel in a westerly direction with a velocity of more
than 100 km/day. However, in general the main epicentres shift in the long run
in a westerly direction along already existing fault planes, with a speed of less
than 1 km/day.
A. R. Ritsema and V. Karnik (1979) have published a review of catastrophic
earthquakes in Europe. They occur in a zone going from Lisbon/Agadir eastward
to North Anatolia/Caucasus. Here more than 25000 deaths have occurred
in the last 25 years. As regards the pros and cons of a warning service for
earthquakes, Ritsema is of the opinion that maintaining good earthquake-resistant
building regulations is better than publishing predictions , since reliable
earthquake prediction is not yet possible.
II. 4.2. Seismicity of the Netherlands
Weak intraplate earthquakes occur in the Netherlands in relation to mostly
buried geological faults. The activity is greatest in South Limburg and decreases
towards the north-west. Most epicentres are in the area of the Peelhorst,
and especially in its south-westerly boundary, the Peelrand . Recently,
levellings across the Peelrand fault demonstrated a continuous creep movement
of the blocks along each other. Earthquakes occur when this creep movement
stops (Ritsema, 1966b).
Seismologists of the Netherlands , Belgium .and Northwest Germany drafted a
seismicity map of Northwestern Europe (Ahorner, Flick, Van Gi/s, Houtgast and
Ritsema, 1976). This study was included in a report (Ritsema ed., 1976) of a
symposium especially devoted to earthquake risks for nuclear power plants situated
in Europe. Ritsema also has published a paper on the probabilities of
occurrence of earthquakes in the region of the North Sea (1980).
H.5. NUCLEAR EXPLOSIONS
Nuclear explosions (Ritsema, 1971, 1973, 1979 and 1980) radiate more energy
in the higher frequences of P waves than do natural earthf]uakes. This is caused
by the smaller source dimensions and smaller rise time in artificial explosions.
The amplitude of the horizontal S waves is very smalI, less surface waves appear,
and the first onset of the P waves is of course an omnidirectional compression
. These criteria among others must be used if one wishes to discriminate
bet ween nuclear explosions and earthquakes. If it is the aim to reach a satisfactory
control of experiments with nuclear weapons, then it will be necessary
to arrange for a more homogeneous distribution of seismographs over the globe
than at present is the case.
II.6. SEISMOLOGICAL RESEARCH IN THE FORMER
NETHERLANDS EAST INDIES
Outside the Netherlands , seismological research was carried out by scientists
from the Netherlands in the Royal Magnetic and Meteorological Observatory
67

11.6.1. Instrumentation at the KMMO
Already before 1898 some small primitive seismographs were used at the Observatory,
which were able to record strong vibrations of the ground. The
seismological research began in 1898 (six years before recording began at De
Bilt), when a Milne seismograph was put into operation ; it then became possible
to check the reports of earthquakes that were frequently felt on the islands
of the Archipelago. Seismographs , designed by the seismologist John Milne,
were in use at many places in the British colonies , but they had only a low
magnification (about 10 times).
A great improvement was the purchase of a Wiechert horizontal seismograph
of 1000 kg, which was installed by C. Braak in 1908. It now became possible
to determine the epicentres of many earthquakes, even by using only the recordings
at Batavia. In 1911 a sm all Wiechert seismograph (100 kg) was set up
at Malabar (about 100 km southeast of Jakarta). The' owner was K.A.R. Bosscha,
administrator of the famous Malabar tea plantation, who had a great interest
in scientific research.
The seismograph collection at Batavia was augmented in 1928 by a vertical
Wiechert seismograph of 1300 kg. As many strong earthquakes occur in the
eastern part of the Archipelago and also earthquakes with a very deep focus,
a large seismograph (1000 kg Wiechert horizontal) was installed in 1925 on the
island of Ambon, south of Ceram. A smaller seismograph was put into operation
some years later near Medan (northeast coast of Sumatra) . The proper functioning
of the seismographs on the islands outside Java took much care. During
strong earthquakes the recording pens were thrown off rat her frequently. A
separate problem was the accurate recording of time on the seismograms, which
was a weak point.
Summary of Seismograph Installation in the former Netherlands East Indies
Year Location
Seismograph Type
1898 Batavia (western Java)
Milne
1908 Batavia
Wiechert horizontal (1000 kg)
1911 Malabar (western Java)
Wiechert horizontal (100 kg)
1925 Ambon Island
Wiechert horizontal (1000 kg)
1928 Batavia
Wiechert vertical (1300 kg)
1929 Medan (northern Sumatra) Wiechert horizontal (1000 kg)
11.6.2. Research results
An important fact for the Observatory at Batavia was the arrival (in 1927)
of H.P. Berlage, who had graduated in Zürich on the theory of seismographs
and who had dealt with the problem of determining the position and depth of
an earthquake centre. The depth of a hypocentre was calculated from the difference
in travel time between the normal P wave and its reflections from the
core and the surface of the earth. In the first years of his stay at Batavia
Berlage wrote an extensive contribution entitled "Seismometrie" for the "Handbuch
der Geophysik"; Band 4 (Beriage, 1932). In this paper a description is
given of the seismoscopes and seismographs known at that time, as weIl as a
treatise on the theory of seismograph magnification. Berlage also dealt with
the determination of an epicentre and methods to calculate the depth of a hypocentre.
(Nowadays these and ot her parameters c.an be calculated much more
69

over the Mid-Atlantic Ridge, bet ween lOoN. and 19°N. Little or no sediment
was found along the Mid-Atlantic Ridge nor along a broad strip on both sides
of it. In the deep basins sediments were found in a few layers with a total
thickness of 2 km. The distribution of the sediments can be explained from
the spreading of the ocean floor, which now takes pIace with an average velocity
of 1. 2 cm per year.
II. 7.3. Suriname
Following the OCPS Project (research on the continental shelf of Suriname,
see section I. 8.1) Collette and co-workers (1971) carried out a seismometricgeomagnetic-gravimetric
survey of the Guiana Plateau and the continental shelf
off the coast of Suriname. Measurements were made on board H.Nl.M.S. Luymes
in 1969 as well as on board the freighter Themis of the SMS (Suriname Shipping
Company). Along eight profiles of about 500 km length the following quantities
were measured: the structure of the sea bottom, the strength of the geomagnetic
field, and the acceleration of gravity. Surprising results were the asymmetric
structure of the Guiana Plateau and the existence of large negative
gravity anomalies on the continent al sheIf north of Suriname.
II. 7.4. Kroonvlag Project: 1967-1980
After the NA V ADO Project (see section I. 8. 2) Collette and his research group
were able to continue the geophysical survey of the Atlantic Ocean in the form
of the Kroonvlag Project, thanks to a subsidy from the Netherlands Organization
for the Advancement of Pure Research (ZWO) and grants-in-aid from
petroleum companies. Through the cooperation of the KNSM and the SMS more
than 40 seismic and geomagnetic profiles were drawn up to the ocean bet ween
the English Channel and Central and South America, at 6°N. up to 37°N. The
structure of the ocean bottom was determined almost continuously by means of
an airgun (Lamont design, improved by Philips). The geomagnetic field strength
was recorded continuously by a proton magnetometer. All data were recorded
on magnetic tape by means of a computer.
The following ships offered hospitality for the research: Luymes, Snellius
and Vidal (all three during the NAVADO Project) and af ter that 17 ships of
the Kroonvlag Company: Achilles , Adonis, Aegis, Arabian Express, Ares,
Aristoteles, Charis, Daphnis, Hathor, Hercules, Herrnes , Marathon, Mercurius,
Osiris, Palamedes, Themis. The courses sailed were mostly in a N.E./S.W. direction,
but in some cases E. IW ., when the ships could deviate from the normal
route (on request).
An enormous amount of data obtained about bathymetry, seismic sounding
and geomagnetism (and in the first years also about gravity) was collected and
processed. Special attention was paid to the fracture zones, which are perpendicular
to the Central Rift of the Mid-Atlantic Ridge. The appearance of these
fracture zones makes the geomagnetic patterns in the Ridge especially complicated.
Already at the beginning of the Kroonvlag Project Collette and Rutten
Figure 35. Topography of the ocean floor in part of the Atlantic Ocean northeast of
Suriname, according to seismic research by the Vening Meinesz Laboratory (State
University at Utrecht). The Atlantic Rif t-zone (see: arrows) runs north-south and
is offset at 15°20'N. by an east-west fault called Fifteen Twenty Fracture Zone. At
12°40'N. another fault, the Marathon Fracture Zone, is shown (Collette et al., 1974b
and 1980). Photo courtesy of the "Stichting Film en Wetenschap" (Utrecht).
72

(1972) tried to find arelation bet ween the direction of the Central Rift, the
pattern of geomagnetic anomalies and the fracture zones. Preliminary results
of the extensive research were embodied in two publications by Col/ette , Schouten,
Rutten and Slootweg (1974a, 1974b).
Col/ette (1975) published a review of the outcome of the investigations carried
out in the years 1964 to 1974 in the Proceedings of the National Geodynamics
Symposium (Amsterçlam, 1975).
Col/ette, Schouten and Rutten (1971) performed a special investigation into
the sediments in the West European Basin, which stretches from the Bay of
Biscay to Ireland, with assistance from freighters of the Kroonvlag Project
(see section 1.8.3). The following five KNSM vessels took part in this investigation:
Themis, Aegis, Hathor , Osiris and Charis . The thickness of the sedimentary
layers was measured as weIl as the intensity of the geomagnetic field.
II. 7.5. Vaarplan (Sailing Scheme) Projects: 1974-1978 and 1978-1982
A new phase in the study of the Atlantic Ocean began when H.NI.M.S. Tydeman
was commissioned in 1977 (see Chapter I, section 1.8.4). This oceanographic
ship was built to replace the hydrographic vessels H. NI.M.S. Snellius
and Luymes and to be used also for civil oceanographic investigations.
The scientific programme contained, among ot hers , the following projects : a
detailed survey of the Mid-Atlantic Ridge, an investigation of the Demarara
Abyssal Plain , and a gravity, geomagnetic and seismic investigation of the Atlantis-
Meteor seamounts complex south of the Azores.
The Marine Geophysics Group of the Vening Meinesz Laboratory began to
investigate as a first object a region southeast of the Azores, in order to study
the influence of sea-bottom topography on the geomagnetic anomalies , as weIl
as disturbances in these anomalies by fracture zones (Twigt . Slootweg and
Collette , 1979). As accurate echo-soundings of the sea bottom are a first requirement
for bathymetry, Slootweg developed the theory and apparatus to
carry out three-dimensional echo soundings at sea , which led to his thesis (1980) .
It is of course intended that the Marine Geophysics Group will use the acousticseismic
echo sounding method , when desirabie , in each fut ure investigation .
II. 7.6. Disposal of radioactive waste
In the year 1979 Collette was asked for advice by the Ministry of Economy
with reference to the problem of burying highly radioactive waste in the bottom
of the ocean. This is an international problem, for which the OECD (Organization
for Economic Cooperation and Development) has set up a Sea-bed Working
Group representing the following six countries: U. S. A., Canada, U. K., France,
Japan and the Netherlands . The question was whether an appropriate place
could be designated in the ocean bottom for burying the strongly radioactive
waste from nuclear power plants and laboratories. A Sea-bed Programme has
been drawn up, based on seismic research of the bottom of the Atlantic Ocean,
which among others was executed by the Vening Meinesz Laboratory . For the
moment it is thought possible to bury this waste in a seismically and structurally
quiet part of a deep ocean basin (and not in a subduction zone) , although
no material has yet been buried. At present the investigation is being continued
by the State Geological Survey at Haarlem.
75

REFERENCES TO CHAPTER 11
Ahorner, L., J.A. Flick, J.M. van Gils, G. Hout gast , A.R. Ritsema (1976) -
First draft of an earthquake zoning map of N. W. Germany, Belgium, Luxemburg
and the Netherlands. K. N.M.1. Publ. 153,39-41,1976.
Berg, A.P. van den, S.A.P.L. Cloetingh, D.J. Doornbos (1978) - A comparison
of PKP precursor data from several seismic arrays. Journ. Geophys., 44,
499-510.
Berlage, H.P. (1924) - Untersuchungder De Quervain-Piccard'schen Seismographen
und einiger allgemeiner seismometrischen Probleme. Dissertatie,
Zürich.
Berlage, H.P. (1932) - Seismometer. Handbuch der Geophysik, Band 4, 299-
526, 1932.
Berlage, H.P. (1937) - A provisional catalogue of deep-focus earthquakes in
the Netherlands East Indies, 1918-1936. Gerlands Beitr. zur Geophysik,
50,7-17,1937.
Cara, M., A. Nercessian and G. Nolet (1980) - New inferences from higher mode
data in Western Europe and Northern Eurasia. Geophys. Journ. Roy. Astr.
Soc., 61, 459-478.
Cloetingh, S.A.P.L., G. Nolet and M.J.R. Wortel (1979) - On the use of Rayleigh
wave group velocities for the analysis of continent al margins . Tectonophysics,
59, 335-346.
Cloetingh, S.A.P.L., G. Nolet and M.J.R. Wortel (1980a) - Crustal structure of
the Eastern Mediterranean inferred from Rayleigh wave dispersion . Earth
Plan. Sci. Lett., 51, 336-342.
Cloetingh, S.A.P.L., G. Nolet and M.J.R. Wortel (1980b) - Standard graphs
and tables for the interpretation of Rayleigh wave group velocities in crustal
studies. Proc. Kon. Ned. Akad . Wet., B 83 (1),101-118.
Cloetingh, S.A.P.L., G. Nolet and M.J.R. Wortel (1980c) - Crustal studies of
the Eastern Mediterranean inferred from Rayleigh wave dispersion . Proc.
"Evolution and Tectonics of the Western Mediterranean and surrounding
areas", Inst. Geograph. Nat., Madrid, Spec. Pap., 201, 259-269.
Collette, B. J ., R. A. Lagaay, A. R. Ritsema and J. A. Schouten (1967) - Seismic
investigations in the North Sea, 1 &. 2. Geophys . Journ. Roy. Astr. Soc. ,
12,363-373,1967.
Collette, B.J., J.1. Ewing, R.A. Lagaay and M. Truchan (1962) - Sediment distribution
in the oceans: the Atlantic bet ween lOoN. and 19°N. Marine Geology
, 7, 279-345,1969.
Collette, B.J., R.A. Lagaay, A . R. Ritsema and J.A. Schouten (1970) - Seismic
investigations in the North Sea, 3 to 7. Geophys. Journ. Roy. Astr. Soc. ,
19, 183-199, 1970.
Collette, B. J ., J. A. Schouten and K. W . R utten (1971) - Sediment distribution
in the West European basin of the Atlantic Ocean. In: Histoire structurale
du Golfe de Gascogne , VI. 7, Ed. Technip, Paris, 1971.
Collette, B.J., J.A. Schouten, K.W. Rutten, D.J. Doornbos and W.H. Staverman
(1971) - Geophysical investigations off the Surinam Coast. Hydrogr.
Newsl. Spec. Publ. 6,17-24.
76

Collette, B.J. and K. W. Rutten (1972) - Crest and fracture zone geometryof
the Mid-Atlantic Ridge between lOoN. and 16°N. Nature Phys. Sciences,
237,131-134,1972.
Collette, B.J., K.W. Rutten, J.A. Schouten and A.P . Slootweg (1974a) - Continuous
seismic and magnetic profiles over the Mid-Atlantic Ridge bet ween
12°N. and 18°N. Marine Geophys. Research. 2,133-141,1974.
Collette, B.J., J.A. Schouten, K.W. Rutten and A.P. Slootweg (1974b) - Structure
of the Mid-Atlantic Ridge Province bet ween 12°N. and 18°N. Marine
Geophys. Res., 2,143-179.
Collette, B.J. (1975) - Fracture zones in the Central North Atlantic: a review
and progress report. In: Progress in Geodynamics, 208-217, Kon. Ned.
Akad. Wet., 1975.
Csikós, I. (1975) - On the theory of the electromagnetic seismograph. Mededelingen
en Verhandelingen van het K.N.M.I .. no. 95 (1975).
Csikós, I. (1975) - A preliminary no te on Scholte's model of the earthquake
focus with a discontinuous stress field. Sci. Rep. no. 13, Proc. Geodyn.
Symp., Amsterdam, 1975.
Doornbos, D.J. and E.S. Huseby (1972) - Array analysis of PKP phases and
their precursors. Phys . Earth Plan. Inter. 5, 387-399.
Doornbos, D.J. and N.J. Vlaar (1973) - Regions of seismic wave scattering in
the earth's mantle and precursors to PKP. Nature Physical Science, 243,
58-61.
Doornbos, D.J. (1974) - The anelasticity of the Inner Core. Geoph. Journ.
Roy. Astr. Soc., 38, 397-415.
Doornbos, D. J. (1974) - Seismic wave scattering near caustics: obervations of
PKKP precursors. Nature, 247, 352-353.
Doornbos, D.J. (1974) - Array analysis of Core phases . Proefschrift, Utrecht.
Doornbos, D. J. (1976) - Characteristics of Lower Mantle inhomogeneities from
scattered waves. Geoph. Journ. Roy. Astr. Soc., 44, 447-470.
Doornbos, D.J. (1977) - The excitation of normal modes of the Earth by sources
with volume change. Geophys. Journ. Roy. Astr. Soc., 51, 465-474, 1977.
Doornbos, D.J. and J.C. Mondt (1979a) - Attenuation of P- and S-waves diffracted
arond the co re . Geophys. Journ. Roy. Astr. Soc. , 57, 353 - 380.
Doornbos, D.J. and J . C. Mondt (1979b) - P- and S-waves diffracted around
the core and the velocity structure at the base of the mantle. Geophys.
Journ. Roy. Astr. Soc., 57, 381-396, 1979.
Eindverslag (1918) - Eindverslag over de onderzoekingen en uitkomsten van
den Dienst der Rijksopsporing van Delfstoffen in Nederland, 1903-1916,
Amsterdam, 1918.
England , F. and R. Wortel (1980) - Some consequences of the subduction of
young slabs. Earth and Plan. Sci. Lett., 47, 403-415.
Gedenkboek (1954) - Gedenkboek van het Koninklijk Nederlands Meteorologisch
Instituut, 1854-1954. Staatsdrukkerij- en Uitgeverijbedrijf , Den Haag.
Kennett, B. L. N. and G. Nolet (1978) - Resolution analysis for discrete systems.
Geophys. Journ . Roy. Astr. Soc., 53, 413-425.
77

Kennett, B. L. N. and G. Nolet (1979) - The influence of Upper MantIe discontinuities
on the toroidal free oscillations of the Earth. Geophys. Journ.
Roy. Astr. Soc., 56, 283-308.
Koning, L. P. G. (1941) - Over het mechanisme in den haard van diepe aardbevingen.
Proefschrift, Amsterdam, 1941.
Koning, L.P.G. (1942) - On the mechanism of deep-focus earthquakes. Gerl.
Beitr. zur Geophys., 58,159-197.
K.N.M.1. (1904-now) - Seismische Registrierungen in De Bilt, Vol. 1 (1904)
- 30 (1942); Seismic Records at De Bilt. Vol. 31 (1943)-now.
Mondt, J.C. (1977) - SH-waves: theory and observations for l:J. > 90°. Phys.
Earth and Planet. Int., 15, 46-59.
Mondt, J.C. (1977) - Full wave theory and the structure of the Lower MantIe.
Proefschrift, Utrecht.
N . T . v. N . I. (1898-1942) - Vulkanische verschijnselen en aardbevingen in den
Oost-Indischen Archipel. Natuurkundig Tijdschrift van Nederlands-Indië,
1898-1942.
Nolet, G. (1975) - Higher Rayleigh modes in W. Europe. Geophys. Res. Lett.,
2, 60-62.
Nolet, G. (1976) - Higher modes and the determination of Upper MantIe structure.
Proefschrift, Utrecht.
Nolet, G. and G.F. Panza (1976) - Array analysis of seismic Surface Waves:
Limits and Possibilities. Pure Appl. Geophys. , 114, 776-790.
Nolet, G. (1977) - The Upper MantIe under Western Europe inferred from the
dispersion of Rayleigh Modes. Journ. Geophys., 43, 265-285.
Nolet, G. (1978) - Simultaneous inversions of seismic data. Geophys. Journ.
Roy. Astr. Soc., 55, 679-691.
Nolet, G., G.F. Panza, M.J.R. Wortel (1978) - An averaged model for the Adriatic
Subplate. Pure Appl. Geophys., 116, 1284-1298.
Nolet, G. and B . L. N . Kennett (1978) - Normal mode representation of multipleray
reflections in a spherical Earth. Geoph. Jour. Roy. Astr. Soc. 53, 219-226.
Ritserna , A. R. (1952) - Over diepe aardbevingen in de Indische Archipel.
Proefschrift, Utrecht, 1952.
Ritserna, A.R. (1954) - The seismicity of the Sunda Arc in space and time.
Indonesian Journal for Natural Sciences, 41-50, 1954.
Ritserna, A.R. (1955) - The fault plane technique and the mechanism in the
focus of the Hindu Kush earthquakes. Indian Journ. Meteor. Geophys.,
6, 41-50, 1955.
Ritserna, A.R. (1957) - On the use of transverse waves in earthquake mechanism
studies. Verhand. 52, Lemb. Meteor. Geof., Djakarta, 1957.
Ritserna, A.R. (1958) - (i,l:J.)-curves for bodily seismic waves of any focal
depth. Verh. 54, Lemb. Meteor. Geof., Djakarta, 1958.
Ritserna, A.R. and J. Veldkamp (1960) - Fault plane mechanisms of Southeast
Asian earthquakes. Meded. en Verhand. K.N .M.I., No. 76,1960.
78

Ritsema, A.R. (1962) - Pand S amplitudes of two earthquakes of the single
force couple type. Bull. Seism. Soc. Amer., 52, 723-746,1962.
Ritsema, A.R. (1966a) - The fault plane solutions of earthquakes of the Hindu
Kush Centre. Tectonophysics, 3,147-163,1966.
Ritsema, A . R. (1966b) - Note on the seismicity of the Netherlands . Kon. Ned.
Akad. van Wet., Proc. Ser. B, 69, 2, 235-239,1966.
Ritsema, A.R. (1969a) - Seismic-tectonic implications of a review of European
earthquake mechanisms. Geol. Rundschau, 59, 36-56, 1969.
Ritsema, A. R. (1969b) - Seismie data of the West Mediterranean and the problem
of oceanization. Verh. Kon. Ned. Geol. Mijnb. Gen., 26,105-120,1969.
Ritsema, A.R. (1970a) - Notes on Plate Tectonics and Arc Movements in the
Mediterranean Region. Proc. XII Gen. Ass. Eur. Seism. Comm., 1970.
Ritsema, A. R. (1970b) - On the origin of the Western Mediterranean Sea Basins .
Tectonophysics, 10, 609-623, 1970.
Ritsema, A.R. (1971,1973,1979) - Seismie detection and identification of underground
nuclear explosions. Working paper Netherlands at C.C .D. no. 323/
416, and C.D. no. 7,1971,1973,1979.
Ritsema, A.R. (1972) - Deep earthquakes of the Tyrrhenian Sea. Geologie en
Mijnbouw, 51, 541-545, 1972.
Ritsema, A.R. (1974a) - General trends of fault plane solutions in Europe.
Proc. General Assembly E.S.C., Trieste, Italy. 379-385,1974.
Ritsema, A.R. (1974b) - The earthquake mechanisms of the Balkan Region,
U.N.D.P.-Project Rem/70/172: K.N.M.1. Scient. Rep. 74-4. pp. 86.1974.
Ritsema. A.R. (1975a) - The contribution of the study of seismicity and earthquake
mechanisms to the knowledge of Mediterranean geodynamic processes.
Progress in Geodyn .• Proc. Nat. Symp. Geod .• Amsterdam. 142-153. 1975.
Ritsema. A.R. (1975b) - Seismie sequences in the European Mediterranean.
Proc. XIV General Assembly E.S.C .• Trieste. Italy. 367-372.1975.
Ritsema. A.R. (1976. editor) - On earthquake risk for Nuclear Power Plants.
K.N.M.1. Publ. 153. pp. 192. 1976.
Ritsema. A.R. (1977) - Seismicity and seismie risk in the Sunda Arc. Proc.
Symp. on the analysis of seismicity and on seismie risk. Liblica. 151-156.
Ritsema. A.R. (1979) - Active and passive subduction at the Calabrian Arc.
Geologie en Mijnbouw. 58.127-134.1979.
Ritsema. A. R. and Z. V . Karnik (1979. editors) - European Catastrophic Earthquakes.
Tectonophysics. 53. 155-337. 1979.
Ritsema. A.R. (1980) - On the assessment of seismie risk in the North Sea
Area. K.N .M.1. Publ. V366. pp. 19. 1980.
Ritsema. A.R. (1980) - Seismische controle op kernwapenproeven. Verslag Afd.
Natuurkunde Kon. Ned. Akad. Wet.. 89. 36-41.1980.
Scholte • J. G . J. (1956) - On seismie waves in a spherical earth. Mededelingen
en Verhandelingen K.N.M.I.. 65.1956.
Scholte. J.G.J. (1958) - Rayleigh waves in isotropie and anisotropic elastic
media. Mededelingen en Verhandelingen K. N .M. 1.. 72. 1958.
79

Scholte , J . G . J. (1961) - Propagation of waves in inhomogeneous media. Geophysical
Prospecting, Vol. 9, 86-115.
Scholte , J . G . J. (1962) - Obliq ue propagation of waves in inhomogeneous media.
Geophys. Journ. 7, 244-261, 1962.
Scholte, J.G.J. and A.R. Ritsema (1962a) - Generation of earthquakes by a
volume souree with moment. Bull. Seism. Soc. Amer., 52, 747-765,1962.
Scholte, J.G.J. (1962b) - The mechanism at the focus of an earthquake. Bull.
Seism. Soc. of America, 52, 711-721, 1962.
Slootweg, A.P. (1980) - Multiple beam generation with a digital computer for
echo-sounding at low and high frequencies. Proefschrift, Utrecht, 1980.
Steketee, J.A. (1958a) - On Volterra's dislocations in a semi-infinite elastic
medium. Canad. Journ. of Physics, 36,192-205.
Steketee, J.A. (1958b) - Some Geophysical Applications of the Elasticity Theory
of Dislocations. Canad. Journ. of Physics, 36,1168-1198.
Steketee, J.A. (1974) Elasticiteitstheorie van Dislocaties . Delft Univ. of Techn. ,
Dept. of Aeron. Eng., Report VTH-179, 1-70.
Steketee, J.A. (1975) - A no te on Elasticity Theory of Dislocations and Earthquake
Mechanisms. Progress in Geodynamics (Roy. Neth. Acad. of Arts and
Sciences),126-137.
Steketee, J.A. (1976) - Elasticity Theory of Dislocations . Proc. 21st Congress
of the Indian Soc. of Theor. and Appl. Mechanics at Bangalore, 85 -100.
Twigt, W., A.P. Slootweg and B.J. Collette (1979) - Topography and a magnetic
analysis of an area south-east of the Azores. Mar. Geophys. Res., 4, 91-
104, 1979.
Veen, H.J. van (1969) - A laser strain seismometer. Proefschrift, Utrecht, 1969.
Vermeulen, J.M. and D.J. Doornbos (1977) - Mantle heterogeneity and mislocation
patterns for seismie networks. Journ. Geophys., 43, 545-559, 1977.
Visser, S. W. (1921) - On the distribution of earthquakes in the Netherlands
East Indian Archipelago, 1909-1919. Verh. Kon. Magn. en Meteor. Obs. te
Batavia, 7, 1921.
Visser, S.W. (1922) - Inland and submarine epicentra of Sumatra and Java
earthquakes. Verh. Kon. Magn. en Meteor. Obs. te Batavia, 9,1922.
Visser, S. W. (1925) - Some researches into the propagation of Seismie Long
Waves. Verh. Kon. Magn. en Meteor. Obs. te Batavia, 16, 1925.
Visser, S. W. (1931) - On the distribution of earthquakes in the Netherlands
East Indian Archipelago, 1920-1926. Verh. Kon. Magn. en Meteor. Obs. te
Batavia, 22, 1931.
Visser, S.W. (1933) - Aardbevingen en getijden te Amboina in 1932. Natuurk.
Tijdschr. voor Ned. Indië, 93,143-147.1933.
Visser, S. W. (1936a) - Some remarks on the deep-focus earthquakes in the
I.S.S. Gerlands Beiträge zur Geophysik, 47, 321-332. 1936.
Visser, S.W. (l936b) - Some remarks on the deep-focus earthquakes in the
I.S.S. Gerlands Beiträge zur Geophysik, 48. 254-267,1936.
80

Visser, S.W. (1937) - Aardbevingen met zeer diepe haard in Nederlandsch Indië.
Natuurk. Tijdschr. voor Ned. Indië, 97,168-172,1937.
Visser, S.W. (1937a) - Aardbevingen met zeer diepen haard. Tijdschrift Kon.
Ned. Aardr. Gen., 54, 313-335,1937.
Vlaar, N.J. (1964) - The seismic pulse in a semi-infinite medium. Appl. Sc .
Res., Bl1, 67-83.
Vlaar, N.J . (19668) - The fjeld from an SH-point source in a continuously layered
inhomogeneous medium, part I: The field in a layer of finite depth.
Bull. Seism. Soc. Amer., 56, 715-724.
Vlaar, N.J. (1966b) - The field from an SH-point source in a continuously layered
inhomogeneous medium, part 11: T he field in a half space. Bull. Seism.
Soc. Amer., 56, 1305-1315.
Vlaar, N . J. (1968) - Ray theory for an anisotropic inhomogeneous elastic medium.
Bull. Seism. Soc. Amer., 58, 2053-2072.
Vlaar, N.J. (1969) - Rays and travel times in a spherical anisotropic earth.
Bull. Seism. Soc. "Amer., 59,1051-1060.
Vlaar, N.J. (1975) - The driving mechanism of plate tectonics: a qualitative
approach. In: Progress in Geodynamics, North Holland Publ. Cy., Amsterdam,
234-245, 1975.
Vlaar, N.J. (1976) - On the excitation of the earth's seismic Normal Modes.
Pure and Appl. Geophys., 114, 863-875,1976.
Vlaar, N.J. and M.J.R. Wortel (1976) - Lithospheric aging, instability and subduction.
Tectonophysics, 32, 331-351.
Vlaar, N.J. and M.J.R. Wortel (1978) - Gravity and the earthquake mechanism.
Phys. Earth and Planetary Interiors, 16,240-246,1978.
Vlaar, N . J. and G. Nolet (1978) - Seismic surface waves. In: Modern problems
in elastic wave propagation, ed. J. Miklowitz, 419-443,1978.
Vlaar, N.J. en G. Nolet (1979) - Het NARS project. Intern rapport, Instituut
voor Aard wetenschappen, Utrecht.
Wortel, M.J.R. and N.J. Vlaar (1978) - Age dependent subduction of oceanic
lithosphere beneath Western South-America. Phys. of the Earth and Plan.
Int., 17, 201-208.
Wortel, M.J.R. (1980) - Age-dependent subduction of oceanic lithosphere.
Proefschrift, Utrecht.
81

Figure 37. F. A. Vening Meinesz with his pendulum gravimeter. Photo by courtesy of University Museum at Utrecht.

CHAPTER 111
Research in gravity
lII.l. THE LIFE WORK OF F.A. VENING MEINESZ - GRAVITY SURVEYS
The third and the youngest field in which Netherlands geophysicists at home
and abroad have become active, is the study of gravity. Whereas in this country
magnetism of the earth had ·already excited interest for centuries, and
earthquake recording had be gun at the beginning of the present century, the
study of gravity in the Netherlands began somewhat later, in the year 1912,
when a young civil engineer, F. A. Vening Meinesz, was appointed to measure
the attraction of the earth by means of gravity pendulums.
Af ter obtaining the degree of civil engineer at the Delft University of Technology
in 1910, Vening Meinesz accepted a post with the Commission on Arc
measurement and Levelling, now known as the Netherlands Geodetic Commission
. He was charged with the task of taking gravity measurements by determining
the oscillation time of a pendulurn, but he was initially hindered in this
work by the motion of the ground, especially in the western part of the Netherlands.
The problem was overcome for the most part by using pairs of pendulums
swinging in the same plane but in opposite directions. In this way the
effect of horizontal accelerations of the ground could be, to a first approximation
, eliminated. He gained his doctor's degree with a thesis written on this
research (Vening Meinesz, 1915).
Between 1913 and 1920 (with an interruption due to illness in 1916/1917)
Vening Meinesz determined at 52 stations the differences in gravity with a reference
station in the Royal Netherlands Meteorological Institute (KNMI) at De
Bilt. Absolute values were obtained by measuring the difference between the
KNMI and the absolute value at the Geodetic Institute of Potsdam . A very detailed
report was published in 1923 (Vening Meinesz, 1923). His widc-spread
interest is demonstrated in the last section of the report, where he makes an
attempt to relate the Bouguer anomalies to the subsurface geology as known
at the time. The results obtained by the State Survey of Mineral Resources indicated
the presence of young Palaeozoic sediments near the surface in the
south-eastern part of the country, and it was surmised that they dipped to
ever greater depths in north-western direction where they were supposed to
be covered by a thick sequence of mainly Quaternary deposits (Eindverslag,
1918). Vening Meinesz remarks, that the gravity anomalies do not support this
general view; they are not smaller in the north-west than in the south-east.
This proved to be a most significant observation , when in the late 1940s and
early 1950s the first geological results of the exploration for oil were obtained.
83

In the mcantime an interesting problem was put forward in international geodesy
circles. An hypothesis arose that the earth resem bIed more a triaxial than
a biaxial ellipsoid. In other words, the equatorial cross-section of the earth
should be somewhat elliptic. Arc measurements in various continents had given
rise to this hypothesis , though this was difficuit to accept from a physical viewpoint.
Arc measurements were not accurate enough to determine the shape of
the earth with the necessary precision ; however, this was possible in fact by
gravity measurements.
The shape of the earth can best be approximated by a geoid; this is the surface
formed by mean sea level in the oceans, which is then extended through
the continents . A very useful mathematical approximation to the shape of the
earth is a biaxial ellipsoid, whose short axis coincides with the pol ar axis of
the earth. The shape of the earth is determined by the position of the geoid
with respect to a standard ellipsoid. This problem can be solved if a sufficiently
dense network of gravity data is available.
Vening Meinesz accepted the task of making many measurements over as large
an area as possible. As the greater part of the earth 's surface is occupied by
oceans, the pendulum apparatus had to be set up on board a ship. The use of
a submarine gave an almost ideal sol ut ion ; at a depth of some tens of meters
the ship's rolling and pitching were so much reduced that an accurate measurement
of the period of the pendulum became possible, and therefore also
the calculation of the value of gravity. Each measurement took half an hour,
during which the oscillations of the pendulurns were recorded. The accuracy
of such a gravity measurement is a few milligals (1 mgal = 0.001 cm/sec 2 ). The
pendulum apparatus, adapted for measurements at sea, was developed at the
KNMI in the years 1923 to 1928. During more than 30 years Vening Meinesz'
pendulum instrument was the best and most accurate sea gravimeter in the world.
In order to solve the problem of the biaxiality or triaxiality of the earth long
series of measurements we re required, along or parallel to the equator or at
least along a good part of it. This is the reason for the long voyages made by
Vening Meinesz, as summarized below. The best known voyage was that of
1934-1935 aboard H.Nl.M.S . K XVIII to the East Indies via Buenos Aires, Cape
Town and Perth. Each time after arriving in the East Indian Archipelago, gravity
measurements were continued, particularly in 1929 and 1930, when the ship
was made available for research purposes for some months.
Vening Meinesz covered in total a distance of several times the circumference
of the earth and carried out more than 1000 gravity measurements. Reports of
these voyages and interpretation of the gravity measurements wcre published
by the Netherlands Commission on Arc measurement and Levelling (Vening
Meinesz, 1932, 1934, 1941 and 1948).
One of the results of these measurements was the denial of triaxiality. There
was no significant ellipticity of the equator. The original reason for these voyages
was therefore answered in a negative scnse. But many important positive
results became apparent.
In the first place it became clear that on the whole the field of gravity values
pointed to a rather weIl balanced situation of the earth 's crust: in general
the isostatic gravity anomalies were found to be small. This result can be interpreted
as follows: the cru st of the earth is floating in equilibrium on the
layers underneath. The isostatic deviations that show up must be ascribed to
tectonic processes that disturb the equilibrium.
Secondly, Vening Meinesz intensively occupied himself with the theory of
gravity in relation to the tectonics of the crust of the earth, and with the reductions
and corrections , necessary to compare the results of the measurements
84

Submarine
KIl
KXIII
KXIII
K XVIII
Vnderwater Pendulurn Surveys by Vening Meinesz
Years Voyage
1923
Den Helder to East Indies via Suez
Canal
1926-1927
To East Indies via Panama Canal
1929-1930
East Indian Archipelago
1934-1935
To East Indies via Buenos Aires
(Argentina) , Cape Town (South
Africa) and Perth (Australia)
Vnderwater Pendulurn Surveys by other Netherlands geophysicists
o 24 1948-1949 Round-trip : Rotterdam to Curaçao
Tijgerhaai
1951
Round-trip : Rotterdam to Curaçao
Zeeleeuw
1956
N ort h Sea (see section 11 I. 5)
Walrus
1957
Pacific and Caribbean near Central
America
with respect to one another (Vening Meinesz, 1929 and 1941) . He broadened
and deepened the theory of tectonic processes in the earth by taking into consideration
the mechanism of thermal convection (Vening Meinesz, 193.4, 1940,
1947) . The value of the viscosity under the earth's crust was determined from
the post-gracial rise of Fennoscandia (Vening Meinesz, 1937).
After an interruption of 10 years due to World War 11, the gravity expeditions
we re resumed (see Tabie) and were aimed at the West Indies and Central
America. Because Vening Meinesz had become Director-in-Chief of the
KNMI , members of his scientific staff as weIl as those of the Department of Geodesy
of the University of Technology (TH) at Delft, participated in these expeditions.
Vening Meinesz' pendulum apparatus was used in 1948 and 1949,
with G. J. Bruins and H. J. A. Vesseur as observers and again in 1951 , when
most of the measurements were made by R. Dorrestein. A report of both voyages
was published in "Gravity expeditions 1948-1958, Vol. V" (Bruins, Dorrestein,
Vesseur, Bakker and Otto, 1960). Technical troubles , which appeared
during these voyages (deposition of salt on the optics of the pendulum apparatus)
prevented complete success.
The purpose of the 1957 expedition , the Ion ge st and the last in which scientific
staff of the KNMI participated, was the study of the Central American
region with its complicated topographic and tectonic structures. Because of
the International Geophysical Year (1957-1958) the submarine H . Nl.M.S. Walrus
was made available for scientific research for more than 5 weeks, in addition
to the voyages to and from the area of research. L. Otto (KNMI) and G .. Bakker
(TH) carried out 64 measurements of gravity ne ar the Pacific coast of Colombia,
Ecuador, Costa Rica and Panama. On the eastern side, in the Caribbean Sea,
15 measurements were made off Colombia and Panama. The report of this expedition
was also published in "Gravity expeditions 1948-1958" (Bruins et al. ,
1960) .
After 1958 the pendulum apparatus was no longer used; it is now displayed
85

creasing pressure waves are formed in the sheet, until a strongly one-sided
downward deviation appears, after a certain limit is passed - downward, because
due to gravity a downward buckling takes less energy than an upward
one. Vening Meinesz' buckling theory was illustrated experimentally by Ph. H.
Kuenen (1936).
Vening Meinesz assumed that mountain building begins with the formation
of a synclinal fOld, followed by downbuckling. Thereafter equilibrium can be
restored by ri se of the folded belt and formation of an elongated chain of mountains.
Volcanism and seismicity are due to tectonic stresses in the region.
The positive gravity anomalies in the deep basins (Soenda, Soela, Banda,
etc.) could be explained by Vening Meinesz by assuming that these basins
sank by convection currents in a plastic layer below the earth's crust, put into
movement by the rising of the folded belt. Indeed, positive gravity anomalies
and subsidence of the earth's surface should appear above downward moving
convection currents.
In his thesis (1954) B.J. Collette investigated in more detail the negative
belt with the adjacent positive zones. Various models of the earth's crust and
various viscosity constants were compared with the observed gravity field.
The buckling hYPQthesis was supported by the geologist J. H. F. Umbgrove
(see: Vening Meinesz, Umbgrove and Kuenen, 1934), who had studied the history
of the Tertiary in the Netherlands East Indies. According to him buckling
of the earth 's crust had taken place in the Miocene period; this was visible on
Timor, the Tanimbar Islands and the Kei Islands. Umbgrove discovered also
traces of Miocene folding on Sumatra and Java and on some islands east of Java.
According to Umbgrove the relief of the deep-sea basins was of post-Miocene
age, and it had been created by downward movement of the bottom of an originally
shallow sea. These observations we re in agreement with the downward
moving convection current, as assumed by Vening Meinesz.
Vening Meinesz was also supported by the geologist and oceanographer
Kuenen (1934), who had participated in the Snellius-expedition (1929-1930,
oceanographic research aboard H. NI.M. S. Willebrord Snellius, of the deep basins
in the eastern part of the Archipelago). As Umbgrove, he too considered
most of the deep-sea basins as sunken continent al areas. The complicated morphology
and tectonics of the East Indian Archipelago were considered by him
to be the result of processes in the original contact zone between Asia and
Australia.
In part 11 of "Gravity Expeditions at Sea" Vening Meinesz interprets the
gravity data in other se as and oceans. Measurements in the West Indies show
a gravity field that has a surprising resemblance to that of the Netherlands
East Indies. In the West Indies too a narrow belt with negative deviations from
the normal gravity is found, flanked by positive areas. The negative belt begins
at the east point of Cuba, runs along the outside of the arc of the Leeward
Islands, then east of the Windward Islands and ends at the coast of South
America. Vening Meinesz assumed that this gravity field is due to the downbuckling
of the crust by compression from the west.
In the coastal region from Venezuela to Haïti a belt of negative anomalies can
be attributed to a compression of the crust in the direction N. 35°E. , caused
by the drifting of South America with respect to the Caribbean region . South
of Panama positive anomalies above deep-sea basins can be compared with positive
areas in the Indonesian Archipelago.
As for the Atlantic Ocean, Vening Meinesz opposed the theory of Alfred Wegener
and based his opposition on the opinion that below continents convective
upward currents must always be present and downward currents below
87

the oceans. This is a consequence of the difference in radioactivity bet ween
continental and oceanic rocks . Therefore Africa and South America for example,
would not drift apart as Wegener stated, but on the contrary would be pushed
towards each other.
In the Mediterranean Sea also Vening Meinesz observed beits of negative
gravity anomalies , which he ascribed to tangential pressure , and positive anomalies
above the deep-sea bas ins . H. P. Cos ter (1945) dealt with these matters
in his doctor's thesis.
111.3. VENING MEINESZ AND THE THEORY OF WEGENER
It has already been mentioned that Vening Meinesz was an opponent of Wegener's
theory. He believed that great continent al displacements , which
according to Wegener took place largely during the Tertiary and Quaternary,
had only been possible in a very early phase of the earth 's history. At that
time the oceanic crust was so plastic because of the high temperature. that the
continent al blocks could move through it . Af ter the Precambrian only limited
movements would have been possible in the crust, such as the formation of
geosynclines and mountain ranges · in the continents and of troughs in the
oceans. In the hook "The Earth and its Gravity Field" written by Vening Meinesz
and W. A. Heiskanen , they treat subjects such as the mechanics of the
earth 's crust. the geophysical history of a geosyncline. and the theory of thermal
convection in the earth. However, they only say of Wegener's theory that
the primeval continent indeed was torn apart by convection currents in the
mantie of the earth, but that this was only possible in the first phase of the
earth 's history (Heiskanen and Vening Meinesz. 1958).
Some years before his death Vening Meinesz (1964) published a 'summary of
his views oh processes in the earth 's crust and mantie , in which a certain rapprochement
to Wegener attracted attention . Impressed by the results of palaeomagnetic
research on rocks from many parts of the world, which pointed to
large horizont al displacements , he came to the conclusion that indeed very large
parts of the crust can disappear by folding and melting; this may change the
position of the continents . However, such a drift of the continents would remain
limited to the orogenic phases in the earth 's history. An almost continual
drift of the continents as taught by palaeomagnetism remained unacceptable
for Vening Meinesz. But he found in the drift of the continents an affirmation
of his hypothesis that convection currents were active in the mantie of the
earth.
111. 4. IMPORT ANCE OF VENING MEINESZ
The life work of Vening Meinesz is of great importance for geodesy as weil
as for geophysics and geology. Many investigators have been stimulated by
his ideas, which were put forward with convincing power. Even those who
could not agree with him in everything were impressed by his mathematical
grasp of the often difficult problems. The international appreciation enjoyed
by Vening Meinesz appears clearly from the "Gedenkboek F. A. Vening Meinesz"
(A. van Weelden, editor, 1957) written as a tribute and presented to him on
the occasion of his 70th birthday. It contains about 30 scientific papers by
geodesists and geophysicists from the international community.
Much of what Vening Meinesz published is still valuable. although some theories
turned out to be less successful. In explaining the beits of negative
gravity anomalies the buckling hypothesis could not stand up to the subduc-
88

tion process in the theory of global plate tectonics. The statement that upward
convection currents must always be present below the continents and downward
currents under the oceans was based on incorrect data about the thermal
balance in and below the crust. However, the major part of his work will remain
of value for a long time.
111. 5. GRAVITY RESEARCH BY OTHERS
East Indian Archipelago. Using the gravity determinations made by Vening
Meinesz in the former Netherlands East Indies during the submarine expeditions
in the years 1923-1930, J.E. Baron de Vos van Steenwijk (1946) calculated
plumb-line deflections and geoid anomalies in the eastern part of the
East Indian Archipelago. The deviations are of course greatest near the beIts
of negative gravity anomalies. Plumb-line deflections up to 40 seconds of arc
were found. Geoid anomalies (elevations of the geoid relative to the standard
ellipsoid) were calculated for a number of stations; values up to 30 metres
were found.
Netherlands . During the Second World-War and also in the years afterwards
many gravity measurements were made by G. J . Bruins and G. L. Strang van
Hees for the State Commission for Geodesy (RCG), and also later by the "Bataafsche
Petroleum Maatschappij" (BPM). Measurements were carried out with
Thyssen and Graf gravimeters, and later on with gravimete-rs of Askania,
Worden and the North American Company, that were based on changes in the
length of a spring and had replaced the cumbersome pendulums. A detailed
map of isogams of Bouguer anomalies in the Netherlands - the resuIt of more
than 26000 measurements - was published by A. van Weel den in the "Gedenkboek
F .A. Vening Meinesz" (1957). In the gravity field of the Netherlands the
buried geological structures are revealed .
North Sea. Vening Meinesz' research in the North Sea was continued by
B. J. Collette (1960) with the aid of the Royal Netherlands Navy, using the
submarine H.Nl.M . S. Zeeleeuw in 1956 and two surface ships, H.Nl.M.S. Vos
in 1955, and H.NI.M.S. Fret in 1957. During the voyages of the Vos and the
Fret the gravimeters (North American) were put down on the bottom of the
North Sea and connected by cable to recorders on the ship. At places where
the sea was too deep the pendulum apparatus of Vening Meinesz was used,
placed in the submarine. The motive for this research was the catastrophic
flood of 1953. Vening Meinesz considered it possible that the subsidence of
the Netherlands could be a reaction to the post-glacial uplift of Fennoscandia,
and this might be verified by gravity measurements. However, Collette's me asurements
did not confirm the theory of Vening Meinesz. Isostatic anomalies
in the North Sea could be explained by geological structures, and no influence
of the rising of .Fennoscandia could be found. This is in agreement with
calculations by J. M. Burgers and B. J. Collette (1958) who studied the glacial
sinking, using a time-dependent model of the earth 's crust.
Caribbean region, Southeast Asia, Europe, North Africa, Andes. Using a
great number of gravity measurements carried out by Companies of Royal
Dutch/Shell, J. W. de Bruyn (1951, 1955) published gravity maps for the Caribbean
region and for Southeast Asia. as weIl as for Europe and North Africa.
J. Hospers and J. C. van Wijnen studied the gravity field of the Venezuelan
Andes and the adjacent basins (1959). They concluded that these Andes were
89

shaped when a southeasterly crustal block was pushed over a northwesterly
part of the earth 's crust.
South America and Caribbean Sea. American geophysicists under the leadership
of M. Ewing carried out, in submarines of the U. S. N avy, hundreds
of gravity measurements along the west coast of South America and in the Caribbean
Sea. Their results were published in the "Gedenkboek" which in 1957
was presented to Vening Meinesz. In 1964 Vening Meinesz gave an interpreta-
Figure 39. Gravity anomalies in the Netherlands . Negative values, especially above
the Cent ral Graben in North Brabant, are due to deeply buried high-density rocks.
A more detailed map was published in the "Gedenkboek F. A. Vening Meinesz" (Van
Weelden, ed., 1957).
90

tion of these results . The formation of the Andes mountains and the deep
trenches in the ocean bottom along the west coast of South America, combined
with negative gravity anomalies along the west coast, was attributed to the
influence of an assumed convection current in the mantle, rising under the
East Pacific Rise and pressing the South American crust in a north-northwestern
direction . Topography as weU as gravity can be compared with that in the
Indonesian Archipelago; the interpretation is essentially the same (Vening Meinesz,
1964).
Suriname. Gravity measurements were carried out also by Veldkamp (1960)
under the program of the International Geophysical Year, in Suriname along
the Marowijne river and along the Paramaribo-Kabel-Dam railroad. These me asurements
can be joined with pendulum measurements by Vening Meinesz performed
in 1949 in the Atlantic Ocean on board H.NI.M. submarine 0 24. The
results of the measurements in Suriname point to a gradual change of continental
crust into oceanic crust north of Suriname. This research was continued
by J.J.G.M. van Boeckel, who measured gravity in north Suriname in the years
1958 and 1960 at about 400 places, which led to a doctor's thesis (Van Boeckel,
1968). Very striking was a large region in Central Suriname with strong negative
anomalies; it was ascribed by Van Boeckel to an enormous granitic batholith
in the crust. lts dimensions are so large that the determinations of the
geodetic locations are disturbed perceptibly. This gravity research was made
posslble by the Netherlands Organization for the Advancement of Pure Research
(ZWO).
OCPS project. Gravity measurements formed also part of the OCPS-programme
(multidisciplinary research on the continent al shelf of Suriname, see Chapter
I, section 8). In 1966 gravity in the western part of this region was mapped
by Strang van Hees, using the sea gravimeter on board the Snellius. The eastern
part of the Suriname shelf was surveyed by Strang van Hees and Vesseur
in 1969 using the hydrographic survey vessel H.NI.M.S. Luymes (Veldkamp,
1967 and 1971). Collette and co-workers (1971) carried out a corresponding
survey on the adjoining Guiana Plateau on board the Luymes; also a number
of profiles we re surveyed with the vessel Themis (SMS). In this project gravity
played an important role.
Netherlands Antilles. R.A. Lagaay (1969) carried out a gravity survey in
the Netherlands Antilles and published the results in his thesis. The gravity
field can be explained by an undulatory deformation of the crust in the transitional
region between continent and ocean. According to Lagaay the intricate
structures in the Caribbean region are controUed by the north-west drift of
South America and by the east-northeast movement of the floor of the Pacific
Ocean. The gravimetrical parts of the theses of Van Boeckel nnd Lagaay were
also published separately by the Netherlands Geodetic Commission (Veldkamp ,
1969). Lagaay's research was subsidized by ZWO.
NAVADO project. In the years 1964-1965 a Netherlands team on board the
hydrographic survey vessel, H. NI. M. S. Snellius, made ten crossings over the
North Atlantic Ocean between 22°N. and 49 0 N. latitude, as part of the program
of the NA V ADO project (see: Geomagnetism, section I. 8.2). On these
voyages gravity was recorded with the aid of an Askania sea gravimeter, developed
for use on surface ships. Under favourable circumstances, dependent
on navigation and location , this instrument reaches an accuracy of a few mgal
91

-
-
o -
.tJ_-
7

Boeckel, J. J. G. M. van (1968) - Gravitational and geomagnetic investigations
in Surinam and their structural implications. Proefschrift, Amsterdam,
1968.
Bruyn, J.W. de (1951) - lsogam maps of Caribbean Sea and surroundings and
of south east Asia. Proc. Third World Petr. Congress, Section Geol. and
Geoph., Leiden, 598-612, 1951.
Bruyn, J.W. de (1955) - Isogam maps of Europe and North Africa, Geophys.
Prospect. 3, 1-14, 1955.
Bruins, G.J., R. Dorrestein, H.J.A. Vesseur, G. Bakker, L.Otto (1960) -
Gravity Expeditions 1948-1958, Vol. V. Atlantic, Caribbean and Pacific
Cruises. Rijkscommissie voor Geodesie, Delft, 1960.
Burgers, J. M. and B. J. Collette (1958) - On the problem of the post glacial uplift
of Fennoscandia. Proc. Kon. Ned. Akad. Wet., Series B 61, 221-241,
1958.
Collette, B.J. (1954) - On the gravity field of the Sunda region (West Indonesia)
. Proefschrift, Utrecht, 1954.
Collette, B.J. (196Ó) - The gravity fieldofthe North Sea. Gravity expeditions,
1948-1958, Vol. V, Rijkscommissie voor Geodesie, Delft, 1960.
Collette, B. J ., J. A. Schouten, K. W. R utten, D. J . Doornbos and W. H. Staverman
(1971) - Geophysical investigations off the Surinam Coast. Hydrograph.
Newsletter, Spec. Publ. Nr. 6, 17-24, Hydrografisch Bureau Kon. Ned.
Marine.
Collette, B.J., J. Verhoef and A.F.J. de Mulder (1980) - Gravity and a Model
of the Median Valley. Journalof Geophysics, 47, 91-98, 1980.
Coster, H.P. (1945) - The gravity field of the Western and Central Mediterranean.
Proefschrift, Utrecht, 1945.
Eindverslag (1918) - Eindverslag over de onderzoekingen en uitkomsten van
den Dienst der Rijksopsporingen van Delfstoffen in Nederland, 1903-1916,
Amsterdam.
Gedenkboek F.A. Vening Meinesz (1957) - Verh. Kon. Ned, Geol. Mijnbouwk.
Genootschap, Geol. Serie, Vol. 18, 1957.
Heiskanen , W. A. and F. A. Vening Meinesz (1958) - The Earth and its Gravity
Field. McGraw-Hill Book Comp. Inc., 1958.
Hospers , J. and J.C. van Wijnen (1959) - The gravity field of the Venezuelan
Andes and adjacent basins. Verh. Kon. Ned. Akad. Wet., Afd. Nat., deel
23, Nr. 1, 1959.
Kuenen, Ph. H. (1936) - The negative isostatic anomalies in the East Indies.
Leidse Geol. Mededelingen, VIII, 169-214, 1936.
Lagaay, R.A. (1969) - Geophysical investigations of the Netherlands Leeward
Antilles. Proefschrift, Utrecht, 1969.
Veldkamp , J. (1960) - Measurements of gravity in Surinam. Gravity expeditions
1948-1958, Vol. V, Rijkscommissie voor Geodesie, Delft. 1960.
Veldkamp, J. (ed.) (1967) - Scientific Investigations on the shelfof Surinam,
Hr. NL. Ms. Snellius (1966). Hydrographic Newsletter, Spec. Publ. Nr.
5, Hydrografisch Bureau Kon . Ned. Marine.
94

Veldkamp, J. (ed.) (1969) - Gravity surveys in Surinam and the Netherlands
Leeward Islands area, 1958-1965. Rijkscom. Geodesie, Vol. 3, Nr. 3, Delft,
1969.
Veldkamp, J. (ed.) (1971) - Scientific investigations on the shelf of Surinam,
Hr. NL. Ms. Luymes (1969). Hydrographic Newsletter, Spec. Publ. Nr. 6,
Hydrografisch Bureau Kon. Ned. Marine, 1971.
Vening Meinesz, F. A. (1915) - Bijdragen tot de theorie der slingerwaarnemingen.
Proefschrift, Delft, 1915.
Vening Meinesz, F.A. (1923) - Observations de pendule dans les Pays-Bas,
1913-1921, Delft.
Vening Meinesz, F .A. (1929 and 1941) - Theory and practice of Pendulum Observations
at Sea, Vol. I, 1929 and Vol. 11, 1941. Rijkscommissie voor Geodesie,
Delft.
Vening Meinesz, F.A. (1932) - Gravity expeditions at Sea, 1923-1930, Vol. I.
Rijkscommissie voor Graadmeting en Waterpassing, Delft, 1932.
Vening Meinesz, F.A., J.H.F. Umbgrove, Ph. H. Kuenen (1934) - Gravity expeditions
at Sea, 1923-1932, Vol. 11. Rijkscommissie voor Graadmeting en
Waterpassing, Delft.
Vening Meinesz, F.A. (1934) - Gravity and the hypothesis of convection currents
in the earth. Verh. Kon. Ned. Akad. Wet., Vol. 37, 37-45, 1934.
Vening Meinesz, F .A. (1937) - The determination of the earth's plasticity from
the post-glacial uplift of Scandinavia. Proc. Kon. Ned. Ak. Wet., Vol.
40, 654- 662.
Vening Meinesz, F.A. (1940) - The earth's crust deformation in the East Indies.
Proc. Kon. Ned. Akad. Wet., Vol. 43, 278-293, 1940.
Vening Meinesz, F.A. (1941) - Gravity expeditions at Sea, 1934-1939. The expeditions,
the computations and the results, Vol. 111. Rijkscommissie voor
Geodesie, Delft.
Vening Meinesz, F .A. (1948) - Gravity expeditions at Sea, 1923-1938. Complete
results with isostatic reduction . Interpretations of the results, Vol.
IV. Rijkscommissie voor Geodesie, 1948.
Vening Meinesz, F.A. (1947) - Convection Currents in the Earth. Proc. Kon.
Ned. Akad. Wet., Vol. 50, 237-245, 1947.
Vening Meinesz, F.A. (1964) - The Earth's Crust and Mantle. Developments
in Solid Earth Physics 1, Elsevier Publ. Comp., Amsterdam, 1964.
Vening Meinesz, F. A. (1964) - Interpretation of gravity anomalies on the west
coast of South America and in the Caribbean. Neth. Geod. Comm., Publ.
on Geodesy, New Series Vol. 2, Nr. 1, 1964.
Vos van Steenwijk, J.E. Baron de (1946) - Plumb-line deflections and geoid
in the Eastern Indonesia, as derived from gravity. Publication of the Netherlands
Geodetic Commission (Delft).
Weel den , A. van (1957) - History of gravity observations in the Netherlands.
Gedenkboek F .A. Vening Meinesz, 305-309, 1957. Verhandelingen KNGMG,
Geol. Serie, deel XVIII.
95

IV.1. POLAR YEARS
CHAPTER IV
Geophysical activity in
international relations
International interest in the polar regions and in the, at that time not understood,
geophysical phenomena that occur there (geomagnetic storms and
aurora) led to the organization of the First International Polar Year 1882-1883.
It was decided that the Netherlands should establish a meteorological and geomagnetic
observatory near Port Dickson, at the mouth of the Jenissei in Siberia.
In 1882 an expedition of 10 persons, under the leadership of M. Snellen (from
the scientific staff of the KNMI), left for the north in the polar vessel·"Varna'·.
Before the fin al destination could be reached, the ship gat stuck in the pack
ice of the Kara Sea and sprung a leak. The expedition wintered on the ice and
was not able to make geomagnetic observations because of the mobility of the
ice. The meteorological program, however, could be carried out.
Attention was also given to the northern lights . At that time scientists w.ere
quite uncertain about the height at which this phenomenon appears. Therefore
an attempt was made to measure the height by observing the aurora
simultaneously at two weil separated places. A few km was thought to be
sufficient, as it was commonly believed that at least some northern lights appeared
at the height of the clouds. Therefore they took with them a telephone
cable of 5 km length plus two phones, so that observations could be made simultaneously.
The reports of the expedition , written by Snellen (1886) and by
Snellen and Ekama (1910) do not mention the results of the parallactic measurements.
They must certainly have failed.
On the whole it can be stated that one of the results of the First Polar Year
was the establishment of a clear relation bet ween the aurora and geomagnetic
storms.
Fifty years later an International Polar Year (1932-1933) was organized for
the second time. A Netherlands expedition of four students (J. van Zuylen,
J.A. de Bruine, H.P.Th. van Lohuizen and K.L. van Schouwenburg) lived for
Figure 42. The staff of the Netherlands Arctic Expedition 1882-1883. Seated at left
M. Snellen (chief of the expedition) and at right L.A.H. Lamie (practical leader and
astronomical observer). Standing, from left to right, H.J. Kremer (physician), J.M.
Ruys (natural philosopher). H. Ekama (physicist) and F. Rust (charged with opening
trade relations). Support staff for the expedition consisted of 5 persons (shipsmate,
carpenter, fireman, cook and engineer).
97

a year at Angmagssalik (East Greenland) and worked through an extensive
program consisting of meteorological and geomagnetic observations , photographs
of the aurora and ionospheric soundings.
The plan to determine the height of the aurora from photographs taken simultaneously
at different stations had only limited success. MosUy, variations
of the auroral forms occurred so rapidly that simultaneous photography proved
to be anillusion; the radio contacts bet ween Angmagssalik and other stations
were insufficient for that purpose .
Thanks to the establishment of a great number of observing-stations in the
polar region, a better insight was obtained into the location of the auroras:
they appeared mostly in a rather narrow belt (the auroral belt) around the
geomagnetic axis of the earth.
The ionospheric research proved the influence of electrically charged particles
(emitted by the sun) on the ionosphere above the polar region. The formation
(nowand then) of a special, intense ionisation (Es) at the height of
the normal E-Iayer, as weU as the polar black out. which is an unusually
strong absorption of radio waves in the polar regions • were discoveries made
during the second Polar Year.
The Greenland expedition and the geomagnetic observations at Angmagssalik
are described in a KNMI publication (KNMI, 1940).
In this second Polar Year another expedition was sent out by the Netherlands
, viz. to Iceland to investigate the troposphere. Netherlands military
pilots, under the leadership of H.G. Cannegieter (from the scientific staff of
the KNMI), carried out twice daily aerological altitude flights near Reykjavik
when weather permitted (Cannegieter, 1932 and 1934). using a meteorograph
lo measure temperatures above Iceland. This succeeded 330 times on 260 days,
and of ten the plane reached a height of more than 6000 m. Moreover , pilot
balloons and radiosondes were flown near Reykjavik, which of ten penetrated
into the stratosphere.
IV.2. GEOPHYSICAL YEARS
Twenty-five years af ter the Polar Year the International Geophysical Year
1957-1958 (lGY) was organized. This time the aim was to study not only the
polar regions by geophysical expeditions • but to include the entire earth. In
the Netherlands scientific interest during the IGY was directed not to the polar
regions • but to its own country and its (former) Overseas Territories.
The KNMI let radiosonde balloons fly to abnormally great heights. The ionosphere
was sounded almost continuously. and on international days drift in
the ionosphere above the Netherlands was investigated by means of radio signals.
Geomagnetic variations were recorded in the Geomagnetic Observatory
at Witteveen . The Astronomical Observatory at Utrecht studied every solar
flare that could be observed. Netherlands weather ships were included in the
oceanographic program through measurements of temperature and salinity.
The Netherlands program was carried out by the following institutions : the
KNMI at De Bilt. the Astronomical Observatory at Utrecht. the Neher Laboratory
of the Netherlands Post al and Telecommunication Services (for study of
the sun and measurements of radio radiation of the sun); the Physical Laboratory
of the Municipal University of Amsterdam (recording of cosmic radiation)
and the Department for Geodesy of the University of Technology at Delft
(measurements of irregularities in the rotation of the earth and oscillations of
the terrestrial globe with respect to the axis of rotation) . The program was
published by the KNMI (1957).
99

100

Outside the Netherlands geophysical research was commenced at Paramaribo
(Suriname) and near Hollandia (former Netherlands New Guinea). At both
places a geomagnetic observatory was established, an ionosphere sounding
station was set up, and a radio telescope was mounted for recording radio radiation
from the sun. These geophysical observations were continued in Suriname
after the IG Y. However, at Hollandia the observations were stopped
aft er granting of sovereignty to Indonesia.
The Department of Geodesy of the University of Technology at Delft organized
an observatory for astronomical-geodetic observations on the Island of
Curaçao, north of Venezuela. During the IGY this observatory was operated
by two geodetic engineers. Results of the observations formed the basis of a
thesis written by one of them (Scheepmaker, 1963).
The Netherlands program for the IGY 1957-1958 was made possible, thanks
to financial aid from the Netherlands Organization for the Advancement of Pure
Research (ZWO).
Observations of the geomagnetic field at Paramaribo and Hollandia were published
in Yearbooks edited by the KNMI. The geomagnetic Yearbooks for Paramaribo
appeared in the series 1957-1967 (Paramaribo, 1957-1967). It is the
intention that this series be continued until 1981 (the recordings of the geomagnetic
field ended in 1981). Yearbooks Geomagnetism from Hollandia were
issued for the years 1957-1962 (Hollandia, 1957-1962). The other observations ,
soundings of the ionosphere at Paramaribo and at Hollandia, were published
by the KNMI in a series of Monthly Bulletins (Paramaribo, 1957-1970, and Hollandia,
1958-1959).
One of the results of the IGY was the discovery of the magnetosphere and
the Van Allen belt. Af ter asolar flare electrically charged particles can penetrate
into the magnetosphere. They become trapped in the Van Allen belt,
and spiral around the geomagnetic field lines back and forth between the northern
and southern hemispheres. As a consequence the aurora appears almost
always simultaneously in both auroral beits.
The great geophysical activity that had come into full swing during the IGY,
was channeled in part into permanent structures after the IGY. Many newly
established observation posts remained in operation. The IGY was timed deliberately
to coincide with a period of extraordinarily great activity of the sun.
In the years following it became evident that results of this research would
gain still more significance if they could be compared with geophysical phenomena
during a sun-spot minimum. This resulted in a plan to intensify anew
the research during the International Quiet Sun Years (lQSY, 1964-1965).
The program for the IQSY was similar to that of the IGY, but was less extensive.
Much attention was paid to the vibrations of the earth 's magnetic field
that are ascribed to the flashing of charged particles back and forth along geomagnetic
field lines. Further, measurements of wind velocities in the ionosphere
raised interest, as weIl as observations of whistlers, long wavelength radio
signals connected with flashes of lightning.
The Netherlands program for the IQSY was adapted to the international program
objectives. Just as during the IGY, the meteorological, astronomical and
geophysical observatories in the Netherlands , and also the geomagnetic ob ser-
Figure 44. The Netherlands Committee for the Second International Polar Year 1932-
1933, and seated, from left to right. the four expedition members: H. P. Th. van Lohuizen,
J. van Zuylen. J.A. de Bruine and K.L. van Schouwenburg (Photo N.V.
Polygoon) .
101

vatory at Paramaribo, took part in the measurements. Investigations during
the IQSY produced further details about discoveries made during the IGY;
this holds especially for the magnetosphere and the Van Allen belt.
IV.3. BELGIAN-NETHERLANDS ANTARCTIC EXPEDITIONS
After Belgium ha.d already sent out four expeditions to Antarctica in 1897,
1958, 1959 and 1960, the Netherlands in 1964 took part in a Belgian-Netherlands
Antarctic Expedition , which wintered at King Baudouin Base, in Queen
Maud Land (south of Cape Town). The program of observations was very extensive.
It consisted of meteorological observations , recordings of geomagnetic
variations , soundings of the ionosphere, observations of aurora and of atmospheric
electricity. Furthermore, the program comprised the following subjects:
geodesy, topography, gravimetry, glaciology, biology and physiology.
The Netherlands participants in the 1964 expedition (J. Rietman, P.M. Buis,
J. van Ameyde and P. Verschoor) were responsible for the meteorological observations.
Also, echo soundings of the ionosphere and measurements of atmospheric
electricity belonged to their program.
This Antarctic research was a continuation of the geophysical activity that
had begun during the IGY. It was organized by the Scientific Committee for
Antarctic Research (SCAR) , which is a committee of the ICSU (International
Council of Scientific Unions ) .
The Belgian-Netherlands program also fitted within the framework of the
IQSY, in which special stress was laid on measurements of atmospheric ozone
and of radioactivity in the air, as a means to investigate movements in the atmosphere.
This might lead to a better insight into the remarkable transition
from winter to summer in the upper air of the polar regions, known as stratospheric
warming.
Twice more (during 1965 and 1966) a Belgian-Netherlands expedition used
King Baudouin Base, each time for one year, to carry out an international
program. Again in these expeditions the Netherlands participants we re responsible
for the meteorological and ionospheric observations. The Netherlands
participants in the expedition of 1965 were: J. Wisse, K. van der Veen, H. Noback
and J. Roest. Participants in the third expedition (1966) were: A.J.
Meerburg , C. Kraan, C. van Vliet and C. Stelling.
The Base was finally closed down in February 1967, and with that an interesting
cooperation between Belgium and the Netherlands in the domain of geophysics
came to an end. The results of the three expeditions , which we re
under the general leadership of Baron Gaston de Gerlache de Goméry, were
published in a series of Yearbooks. The meteorological, geomagnetic and ionospheric
data were for a considerable part collected by the KNMI and published
in its Yearbooks, which are preserved in its Library.
The Belgian-Netherlands Antarctic Expeditions could be carried out thanks
to a large subsidy from the Netherlands Organization for ZWO. Belgium paid
two-thirds of the total cost and ZWO one-third. Not only were three winterings
made possible, but also some summer campaigns in Antarctica, before or after
the winter expeditions .
Figure 45. Observation posts in the Antarctic regions during the IGY or (and)
thereafter. The Belgian-Netherlands expeditions used the King Baudouin Base in
Queen Maud Land in 1964, 1965 and 1966. The grey ring denotes the mean southern
auroral belt.
103

Figure 47. Launching of a meteorological radiosonde at the King Baudouin Base by
members of the Belgian-Netherlands Antarctic Expedition 1964-1965 (Photo Ir. J.
Rietman).
105

The result of the combined investigations of the participating countries can
be summarized as follows. The meteorological observations led to an insight
into the balance of heat in the Antarctic atmosphere. The strong radiation of
heat by the icecap is compensated by the meridional transport of warmer air
through the troposphere. This process is accompanied by downward air movements
above Antarctica. The rim of the continent is characterized by a stormy
climate, caused by squalls and by astrong activity of atmospheric lows around
the icecap. The meteorological as well as the other geophysical observations
(ionosphere, geomagnetism, aurora, atmospheric electricity) show that only a
synoptic study of the data from all Antarctic stations can lead to a good insight
into the processes. The observational data will provide food for study
for many decades.
A general account of the work carried out during a wintering in Antarctica
has been written by Van der Veen and Wisse (1967).
IV.4. THE UPPER MANTLE PROJECT (UMP)
In 1960, after the IG Y, a specialorganization , the Upper Mantle Project
(UMP), was set up to investigate the solid earth, in particular to study the
outer mantle of the earth and the influence exerted by it on the earth 's crust.
In the Netherlands some groups took part in the UMP by studying the following
themes.
a. Mechanisms of earthquakes with epicentres located in Indonesia, Japan,
Europe, Hindu Kush, the Mediterranean region and the Mid-Atlantic Ridge.
b. Geomagnetism in the North Atlantic Ocean, the Netherlands Antilles and
Suriname.
c. Palaeomagnetism of rocks from Sweden, Germany, Spain. Sardinia. Alps.
India and Iceland.
d. Gravity measurements in the North Atlantic Ocean, in the North Sea, the
Antilles and Suriname.
e. Movements of the earth 's crust in the Netherlands , determined from geodetic
measurements.
f. Measurements of the heat flow through the floor of the North Atlantic
Ocean.
g. Geochemistry and radiometrical datings in Suriname, Scandinavia and the
Iberian Peninsuia .
h. Geotectonics in the Mediterranean Region and Scandinavia.
Investigations under a, b, c, d and f have been discussed earlier in Chapters
I, 11, 111. None of the investigations was started by the Netherlands Committee
for the UMP; they were organized by the interested Institutes. However, the
UMP had a stimulating effect. not in the least by the contacts between researchworkers.
The UMP ended in 1971. The Netherlands part was embodied in the Final
Report of the Netherlands Committee for the Upper Mantle Project (KNAW,
1971) •
IV.5. THE GEODYNAMICS PROJECT (GP)
In 1970 the aim of the UMP was defined more precisely as the investigation
of dynamical processes in and below the earth 's crust. This entailed a change
of name; the UMP was converted into the Geodynamics Project (GP). Movements
of the plates into which the lithosphere is divided, were to be studied by
106

means of data from both seismology and palaeomagnetism. Moreover , plutonic
rocks would be studied in special laboratories for a better understanding of
the geodynamic properties of rocks in the outer mantle .
A preliminary report of the Netherlands investigations can be found in the
publication "Progress in Geodynamics" (KNAW , 1975). In this collection of papers
the following are of geophysical character: geomagnetic beits (As), sat-
Figure 48. Measurement of wind movements in the ionosphere above Suriname (1965).
Rockets with built-in sodium ovens were launched from the airfield of Coronie in a
southerly direction . The $Odium trails were visible to a height of more than 100 km.
Observation posts were situated at Paramaribo. Zanderij and Brownsweg.
107

ellite geodesy (Aardoom) • movements in the earth's crust (Baarda, Van Mierlo),
dislocation theory and earthquake mechanisms (Steketee), model of an earthquake
focus with a discontinuous stress field (Csikós), seismicity and earthquake
mechanisms in the Mediterranean region (Ritsema), rotation of Italy
according to palaeomagnetic data (Van den Berg), anisotropy of magnetic susceptibility
(Van den Ende), structural history of the India-Pakistan subcontinent
(Wensink), fracture zones in the Mid-Atlantic Ocean (Collette) , mechanism
of plate tectonics (Vlaar). Most of these investigations have been
mentioned in previous chapters ..
Figure 49. A Nike-Apache rocket ready to be launched for a study of winds in the
ionosphere above Suriname (photo R. V.D., Paramaribo).
108

IV.6. WIND MEASUREMENTS IN THE IONOSPHERE ABOVE SURINAME
(SEPTEMBER 1965)
In Chapter I, section 4, it was stated that wind movements in the ionosphere
can be derived from the fading pattern of radio waves reflected from the ionosphere
(see: Vesseur, 1970) and that for this purpose a fading receiver had
been operated at Paramaribo (Suriname) from January 1971 until September
1972.
As interpretation of fading records depends on some assumptions , it was
earlier decided to test the fading method by means of sodium trails produced
in the ionosphere by rockets . ft appeared feasible to carry out this experiment
in Suriname. An agreement with NASA was reached, approval of the Suriname
government was obtained, and a subsidy was promised by the Netherlands
Organization for Pure Research (ZWO).
Four rockets (Nike-Apache) were made available by NASA free of charge.
Figure SO. A sodium trail, emitted by a rocket above Suriname, shows strong horizontal
winds and wind shears, alternated by turbulent layers, at heights bet ween 90
and 110 km.
109

Hollandia (1958-1959) - Monthly Bulletin on Ionospheric etc. Data, Hollandia,
Netherlands New Guinea. K.N .M.I., De Bilt.
K. N . A. W. (1971) - Upper Mantle Project, Final Report of the Netherlands Commission.
Kon. Ned. Akad. van Wetensch., 1971.
K.N.A.W. (1975) - Progress in Geodynamics, Geodynamics Project, Scientific
Report no. 13 by A.R. Ritsema ed. , Kon. Ned. Akad. van Wetensch.,
1975.
K.N.M.1. (1940) - Magnetische waarnemingen te Angmagssalik gedurende het
Internationaal Pooljaar 1932-1933. K.N.M.1. publicatie no. 98, De Bilt,
1940.
K.N.M.1. (1957) - Het Internationaal Geophysisch Jaar 1957-1958. Verspreide
Opstellen no. 4, K.N .M. 1., De Bilt.
Paramaribo (1957-1967) - Yearbook Geomagnetism, Paramaribo, Surinam.
K.N.M.I., De Bilt.
Paramaribo (1957-1970) - Monthly Bulletin on Ionospheric etc. Data, Paramaribo.
K.N.M.I., De Bilt.
Scheepmaker, A. C. (1963) - Analyse van de waarnemingsresultaten verkregen
op het Geodetisch Astronomisch Station op Curaçao tijdens het Internationaal
Geofysisch Jaar 1957-1958. Proefschrift, Delft, 1963.
Sevensma, H. W . N. (1968) - Metingen aan de ionosferische wind boven Suriname
in september 1965 met behulp van natriumsporen. Publicatie van het
Sterrekundig Instituut der Rijksuniversiteit te Utrecht , nr. 1968/2.
Snellen, M. (1886) - De Nederlandsche Pool-Expeditie 1882-83. Firma Bosch en
Zoon, Utrecht. (Library KNMI)
Snellen, M. en H. Ekama (1910) - Rapport sur l'expédition polaire néerlandaise.
Utrecht, 1910. (Library KNMI)
Veen, K. van der, en J.A. Wisse (1967) - De Belgisch-Nederlandse Antarctische
Expedities. Diligentia voordracht. K. N . M.l., De Bilt, 1967.
Vesseur, H.J.A. (1970) - A correlation apparatus for the measurement of the
drift in the ionosphere by the spaced receiver method. Journ. Atm. Terr.
Physics, 32, 829-835, 1970.
111

y W. Bosrna, S. B. Kroonenberg, R. V . van Lissa, K. Maas and E. W. F. de Roever.
It will appear in "The Geology of Suriname" (GMD, Suriname, Mededeling 27).
V.4. GEOPHYSICAL SURVEYS IN THE NETHERLANDS
V.4.1. Gravity research in the Southeast Netherlands by Government Agencies
During the years 1941 to 1944 the Geophysical Service of the State Mines
carried out a gravity survey in the southeastern part of the Netherlands , in
South Limburg and in the eastern part of North Brabant. The leader of this
survey was L. U . de Sitter. The aim was to determine, if possible, the position
of the major faults and of the related smaller faults, in view of assessing mining
possibilities in the coal field of the Peelhorst region. Students who carried out
the measurements were protected against the "Arbeitseinsatz", this means forced
labour by the German occupational forces. The instruments used in the gravity
survey were Askania torsion balances and Thyssen gravimeters, made available
by the BPM. The observations we re made by the geologists A. Maaskant and G.
Zijlstra, assisted by W.J. van Riel, J.A.M. Schmedding and F. Winkelaar.
During the war years the Netherlands Commission for Geodesy organized
measurements in the southeastern part of the country. W. Nieuwenkamp was
the leader of a party which established a rather dense network of Thyssen
gravimeter stations in North Brabant and North Limburg during the years
1942 to 1944. The results of these measurements were combined with the above
mentioned survey by the Geophysical Service of the State Mines.
The reason for the intensive use of torsion balances in the gravimetric survey
was the following. The torsion balance gives the horizont al gradient of
the acceleration due to gravity, and reacts therefore strongly to the more or
less vertical faults.
Strictly speaking, a unique interpretation of a gradient profile is possible
only in simple cases, when only one discontinuity plane is present. Since the
fault structure in the Southeastern Netherlands is complicated and, moreover ,
the densities of the deeper rocks are not sufficiently well-known, quantitative
analysis of the measurements is not always possible, although in many cases
the model of only one discontinuity plane is sufficient. The fin al report of the
survey appeared in the series "Mededelingen van de Geologische Stichting"
(De Sitter and co-workers, 1949).
V.4.2. Mining possibilities in the Peel Field (North Brabant)
As early as 1905 the geologist and mining engineer W . A. J . M. van Waterschoot
van der Gracht surmised a very gentle and wide topographic swell running
south-east to north-west in the eastern part of the province of North Brabant
to be the surface expression of a horst-like structure in the subsurface. Subsequent
drilling by the State Survey of Mineral Resources led to the discovery
of the Peel Horst with rather shallow Carboniferous coal measures (Eindverslag,
1918). At the time, however, it was considered unadvisable to develop
this field. The matter was taken up again in 1952, when the Minister of Economic
Affairs installed the "Peelcommissie" with the instruction to advise,
whether it would be recommendable to develop the Peel Field in the near fut ure .
The committee was chaired by the professor of mining technology Th. R. Seldenrath
of the University of Technology at Delft; the investigation, seismic
114

eflection and drilling, was supervised by the Geophysical Survey of the State
Mines and the Geological Bureau of the Mining Area.
Between 1952 and 1959 a detailed seismic survey was carried out over an
area of 255 km 2 with a total length of more than 300 km reflection profile. The
drilling pro gramme , consisting of 7 boreholes, was begun before the completion
of the seismic investigation. The Upper Carboniferous was cored; in addition
to the usual physical logs, water tests and temperature measurements
were taken. In 1962 the "Peelcommissie" came to the conclusion, that building
a mine could not be considered recommendable, due not only to technical and
economical considerations, but also due to the discovery in 1959 of large reserves
of natural gas in Groningen and cheap domestic production of oil and
coal and cheap imports. The final report was published in 1963 (Peelcommissie,
1963).
As a consequence of the sharp increases in oil prices during the 1970s the
outlook changed again. On October 4, 1979, on the initiative of the professor
of geology at the Mining Department of the University of Technology J . J. Dozy,
a symposium was held at The Hague (Symposium, 1979). It concerned the coal
measures in the Netherlands subsurface as a possible fut ure source of energy.
The outcome was to make an inventory of the coal reserves in the structuraUy
high parts of the country to a depth of 1500 metres. Seismic field work commenced
in 1981 by the Groundwater Survey TNO under supervision of N. de
Voogd.
V. 4. 3. Geophysical survey in the province of Limburg
In 1979 and 1980, the Geological Surveys of the Netherlands , Belgium and
West Germany carried out a joint geophysical and geological investigation in
the southern part of the province of Limburg and in the adjoining regions of
Belgium and West Germany. The aim was to obtain new information on the structure
of the subsurface in this area, and to stimulate thinking on new hydrocarbon
and metal prospecting possibilities. Gravity measurements at almost
1000 places were carried out with Lacoste-Romberg gravimeters. The tot al intensity
of the geomagnetic field was measured with a Geometrics proton magnetometer.
AdditionaUy, the density of samples from about 50 borehole cores
was determined. A report with detailed maps written by M. J. M. Bless, P. van
Rooyen et al. (1980) was published in the series "Mededelingen Rijks Geologische
Dienst" (Heerlen). The data obtained in this gravity and geomagnetic
survey fit very weU into the already existing picture. Geological and geophysical
considerations lead to the hypothesis that the investigated area may contain
evaporite deposits within the Devono-Dinantian sequence.
V.5. GEOPHYSICAL EXPLORATION IN
THE NETHERLANDS BY OIL COMPANIES
V.5.1. Discovery of the Schoonebeek oil field
Whereas geophysical research in the Netherlands was carried out before and
during the war, namely gravity measurements by BPM (see: Chapter 111, section
111.5.) and geomagnetic measurements by KNMI (see: Chapter I, section
1.2. ), detailed maps were published only later (geomagnetic maps by Veldkamp ,
1951, gravity maps by Van Weelden , 1957).
The gravimetrical survey by Bataafsche Petroleum Maatschappij in 1935 to
1937 led to the discovery of the Schoonebeek oil field (V.P. Ulrich, 1956). The
115

Holland in 1953 to 1958. Only after the development of multiple seismometry
and shot hole techniques could the difficulties be overcome. In East Netherlands
the presence of rock salt made it difficult to obtain data from the layers
below the rock salt, because of the low velocity of seismic waves in the salt
and the attendant strong absorption of seismic energy. Nevertheless in the
1950s a number of gas fields were discovered in the province of Overijssel
that produce from a dolomite below the rock salt deposits.
V. 5. 2. Discovery of the Groningen gas field
Improvement in seismic reflection techniques enabled a more reliable delineation
of geological structures at great depth. Interpretation of drilling results
and improved seismic control led to discovery of gas at Slochteren (near the
town of Groningen) in 1959. This discovery was made by using simple shot
hole and geophone pattern techniques. It was possible to correlate the structure
of the subsurface from one well to another without too much difficulty.
In 1962 seismics and drilling had improved the knowledge of the subsurface
to such an extent that the province of Groningen was seen to have a "giant"
within its boundaries, comparabie with the Panhandle-Hugoton gas field in the
U . S. A. . Mapping of the field was greatly aided by the high signal-to-noise
ratio of the reflection data in the Groningen area. Use of sophisticated processing
techniques for analyzing seismic records was unnecessary in this area.
The Groningen gas field was discussed at a Symposium held in 1968. The
geophysical exploration and delineation was described by D.M. W. te Groen and
W. F. Steen ken • The proceedings of the lectures held at the Symposium were
published in "Verhandelingen van het Koninklijk Nederlands Geologisch Mijnbouwkundig
Genootschap" , Geological Series, Vol. 25, 1968.
The extraction of huge quantities of natural gas from the field causes subsidence
of the subsurface. Knowledge of the amount of subsidence is of course
important in a country were a continuous struggle against the sea is necessary.
The Netherlands Oil Company (NAM), which exploits the Groningen gas
field, carried out levellings across the field in 1964/1965, 1968/1969, 1972,
1975, 1978 and 1981. Almost the entire surface of the province of Groningen
(2400 km 2 ) proved to be gradually sinking. Since the beginning of gas production
in 1965, a surface subsidence of 12 cm has occurred in the centre of the
field. It is expected that finally a value of 30 cm will be reached. Reports on
the subsidence were published by the "Meetkundige Dienst van de Rijkswaterstaat"
(1979 and 1982, Delft).
The discovery of the huge gas field in Groningen stimulated interest to a
great extent. Before, NAM was the only operator; in the 1960s a number of
foreign companies took part in the exploration. This resulted in the present
knowledge of the richness of natural gas. Geological results of seismics and
drilling by NAM and others were presented in four tectonic maps of the Netherlands
continent al area (Heybroek, 1974) that also were published in the
Scientific Atlas of the Netherlands (Anonymous, 1963 to 1977), and in the
Stratigraphic Nomenclature of the Netherlands (Nederlandse Aardolie Maatschappij
and Rijks Geologische Dienst, 1980).
V. 5. 3. Geophysical research at the KSEPL (Rijswijk, South Holland)
Discovery of the natural gas field in Groningen gave rise to research on the
permeability of gas-containing sandstone formations by the KSEPL (Royal
Dutch/ Shell Exploration and Production Laboratory , at Rijswijk, South Holland).
118

J. J. Staal and J. D. Robinson (1977) succeeded in constructing profiles of permeability
by measuring the damping of seismic waves. E. C. A. Gevers and S. W.
Watson (1978) used the acoustic impedance to identify lithologic units and to
estimate the pore fillin g of a reservoir rock. Also G. T. F. R. Maureau and D. H.
van Wijhe (1979 and 1980) developed a method to calculate the position and the
porosity of Permian carbonate rocks in East Netherlands from the acoustic impedance
of seismic waves.
Several geophysicists of the NAM and the KSEPL published contributions
to research methods. Improvement of the signal-to-noise ratio by combining
seismometers, by favourably locating shot· holes and by filtering seismic signals,
was described by G.H.F. Snijders (1958). J.Ph. Poley (1964) investigated
theoreticaUy as weU as experimentally the influence of the critical angle
of reflection on the amplitude of reflected seismic waves. H. van Deemter and
A. W. H. van der Kallen (1978) demonstrated that a very complicated structure
of oH-bearing layers can be unraveled with the aid of three-dimensional seismics.
J . K. Huysinga and A.R. BiddIe (1978) published a method for obtaining
a three-dimensional picture of the bottom of the North Sea by drilling and shallow
seismics.
V. 5. 4. Exploration of the North Sea continental shelf
Af ter the discovery of the Groningen gas field the North Sea was included
in the geophysical research. This began in 1961 with an aerial geomagnetic
survey, carried out by the oH qompanies in a joint venture. A gravity survey
in the North Sea was made initiaUy by means of diving beUs, but these we re
soon replaced by sea-bottom gravimeters, which were connected by cables to
a ship.
Af ter partition of the North Sea shelf among the adjacent countries, exploration
was taken in hand on a large sc ale by seismic investigation and drilling.
It became evident that in the North Sea great variations of the solidity of the
bottom sediments occur within smaU distances , e. g. because old glacial valleys
are filled with unconsolidated sediments. The right choice for the frequency
radiated by the air gun is essential for a sufficient penetration of the seismic
signal into the sea floor.
Exploration techniques and results have been presented and discussed in
international conferences:
- 1975, Reading, England . Petroleum and the continental shelf of North- west
Europe.
- 1981, London. Petroleum geology on the continental shelf of North-west
Europe.
- 1982, The Hague. Petroleum geology of the southeastern North Sea and
adjacent onshore areas.
V.6. HYDROGEOLOGICAL RESEARCH IN THE NETHERLANDS
V.6.1. Water supplies
During preparations to reclaim the IJsselmeer (former Zuiderzee) it appeared
necessary to investigate the salt percentage of the deeper ground water in
the sand layers under the IJsselmeer. Knowledge of this salinity was important
with a view to the ooze that might appear in future polders after reclamation
, and also in relation to the winning of fresh drinking water. The salinity
in the botto!ll of the IJsselmeer was investigated by a geoelectric method to a
119

depth of 250 to 350 meters, under the leadership of A. Volker (Dienst der
Zuiderzeewerken) .
Even before the present polders we re drained, the relative distribution of
fresh and brackish water in the bottom could be calculated. The specific resistance
of the bottom was determined by the Schlumberger method by means
of a movable cable that contained contacts for the electric current and electrodes
for measuring the resistance of the bottom. In spite of the fact that
the cable had contact also with the overlying layer of fresh water, Volker
proved that its influence on the apparent resistance of the soil underneath
the bottom of the lake could be neglected.
Investigation of the IJsselmeer was carried out in the years 1951 to 1955,
and published in 1957 by J. Dijkstra and A. Volker. The results of these
measurements were interpreted with the aid of resistance functions calculated
for a great number of modeis , foUowing the methods of O. Koefoed (see section
V. 7. ). The depth of the boundary between fresh and salt water, which was
calculated from the resistance values, was confirmed by drilling. Geoelectric
exploration was also carried out in the Lauwerszee and in the Waddenzee,
north of Groningen.
The great success of the geoelectric method in the IJsselmeer led in 1954
to the establishment of the Geoelectric Research Working Group of the Central
Organisation for Applied Scientific Research (TNO). In 1967 the activities of
this group we re combined with the hydrogeological mapping of the Netherlands ,
which -was begun by TNO on request of "Rijkswaterstaat". The geological,
hydrological and geophysical researches were incorporated in the "Dienst
Grondwaterverkenning" (Groundwater Survey TNO, DGV) , with W .A. Visser
as first director. He was succeeded in 1972 by F. Walter.
The aim of DGV is mapping the distribution of the groundwater by combining
existing data with geoelectrical surveys and borehole measurements. In this
research the electrical resistance and the natural electric potentialof the rock
penetrated are measured, as weU as the natural y-radiation (as a lithological
characteristic), and the acoustic velocity as a measure of porosity (by means
of the sonic log).
In the framework of the technical assistence to developing countries, the
DGV carries out geoelectric investigations in Pakistan, Africa (Sudan and
Kenya) and in Central America (Colombia and Jamaica) with the intention to
improve irrigation and the supply of drinking water. For that purpose geoelectric
prospecting is complimented by gravimetric reconnaissance and seismic
refraction (Jaarverslag DGV, 1980).
V. 6. 2. Geothermal energy
As a result of extensive seismic research by oil companies, the subsurface
of the Netherlands is rather weU-known to a depth of 3 to 4 km. The presence
of porous and permeable sandstone formations at great depth and at rat her high
temperatures (increase of 30°C to 35°C per km depth) made attractive the idea
of extracting geothermal energy. In 1974 the Central Organisation TNO formed
an Earth's Heat Working Group, with the task of drawing up a report on the
possibility of obtaining geothermal energy from the deep layers in the subsurface
of the Netherlands.
Investigations commenced in 1980 and as geology, hydrology and geophysics
are involved, the execution of the program was entrusted to various institutes:
DGV of TNO, the State Geological Survey, and the Vening Meinesz Laboratory
for Geophysics and Geochemistry (Visser, 1978 and 1979). W. van Dalfsen
120

(DGV) made an extensive investigation of the temperature field in the subsurface
of the Netherlands (up to 400 m depth) , by means of measurements
in II great number of shallow boreholcs (Van Dalfsen, 1980). The temperatures
at great depths (at 500 to 3000 m) were compiled by S. Prins (State Geological
Survey) and pubIished in the Atlas of Subsurface Temperatures in the
European Community (E. Haenel, ed., 1980).
As for a geothermal energy project, it is proposed to drill a test weil in
Delfland (northwest of Rotterdam), we re saline water of about 90°C is present
in sandstone layers at a depth of 2500 metres. For instance, this hot
water might be used for heating hothouses in the area of Westland.
V. 7. EXPLORATION GEOPHYSICS AT THE
UNIVERSITY OF TECHNOLOGY (TH) AT DELFT
Geophysical research in aid of mineral exploration was tackled at the TH
for the first time by J. A. A. Mekel, professor of geology at the TH from 1929
to 1940. (In 1942 he was executed because of activities against the German occupation
forces.) Mekel obtained his doctor's degree in 1928 with a thesis in
which gravity research was appIied to tectonic problems (Mekel, 1928). In the
practical application of gravimetry he especially used the torsion balance, as
a means for studying fault zones.
V. 7.1. Geoelectrical researchby O. Koefoed and co-workers
After Mekel, exploration geophysics at the TH at Delft was undertaken by
O. Koefoed. Koefoed has appIied himseIf with his students to the development
of geoelectrical and electromagnetic sounding methods. The scientific papers
that he produced, alone or with co-workers, were pubIished in the journals
"Geophysical Prospecting" and "Geoexploration", and issued in a special pub­
Iication "Collected Papers, 1952-1980" (Koefoed, 1980). In 1965 he was awarded
the Conrad Schlumberger prize by the European Association of Exploration
Geophysicists, for outstanding contributions to appIied geophysics. Nine theses
were achieved under his leaders hip .
The greater part of the papers published by Koefoed and co-workers are
devoted to electrical sounding methods. The oldest is the method whereby a
direct current is put into the ground while the potential difference bet ween two
points on the earth's surface is measured. By varying the distance bet ween
the points where the current enters and leaves the surface , the dependence
of conductivity on depth can be determined from the measurements. The apparent
electrical resistance of the layered subsurface is compared with resistance
curves calculated for various models of layered structures. Initially
Koefoed used this indirect method (Koefoed, 1955), which gave rise to the theses
of J. C. van Dam (1964) and F. G. van der Hoeven (1964).
According to a direct method, developed by Koefoed and ot hers , the apparent
resistance is expressed in an integral equation , in which the integrand
contains akernel determined by the layering and the conductivity of the subsurface.
In order to interpret the apparent conductivity, the kernel, derived
from the measurements of the electrical resistance, is compared with kernel
functions calculated for various models of conductivity.
After the introduction of a semi-direct method (Koefoed, 1965a), which was
appIied with the Schlumberger arrangement of the electrodes as weil as with
the Wenner method (Koefoed, 1965b and 1966), he found a fast method to investigate
the lamination of the ground, namely by a transformation of the kernel
(Koefoed, 1969 and 1970).
121

A major improvement in the method was reached by D. P. Ghosh, who applied
in his thesis (Ghosh, 1970) the theory.of linear filtering to the problem of
determining the electrical resistivity of a layered subsurface. This improvernent
is based on the fact that the spectrum of the kernel function in the integral
equation for the apparent resistance does not contain high frequences,
from which the calculation can be greatly simplified. Next, Koefoed developed
a very fast method for interpreting resistance measurements at the sacrifice,
however, of maximum accuracy (Koefoed, 1976a and 1976b).
In the book "The application of the Kernel Function in interpreting geoelectrical
resistivity measurements" (Koefoed, 1968) he explains how to derive the
kernel function from the resistivity measurements by a practical procedure,
and how the kernel function can be interpreted for a series of layers with different
resistance. A complete survey of the theory and methodology of electrical
resistivity measurements, including ways to derive the layer parameters
from the apparent resistivity, can be found in the book "Geosounding PrincipIes,
1. Resistivity Sounding Measurements" (Koefoed, 1979).
V. 7.2. Electromagnetic sounding research by O. Koefoed and co-workers
In electromagnetic soundings electric currents are induced in the earth
by a (generally vertical) alternating magnetic field. The induced fields are
detected by electrodes . The distances bet ween the transmitter, the induction
coU, and the surface of the earth are varied, as weIl as the frequency of the
alternating field.
Koefoed and co-workers first directed their attention to induction by an alternating
electromagnetic field in a semi-infinite plate, as a model of a dyke.
They coneidered this as a theoretical problem (Koefoed and Kegge, 1968) and
as a subject for experiment al research (Koefoed and Struyk, 1969).
The electromagnetic sounding method has led to some publications and doctor's
theses. The thesis of R.A. Bosschart (1964) deals with measurements
with a fixed or a moving source of the electromagnetic alternating field. The
induced field depends on the structure of the subsurface , the resistivity of
the layers, and the frequency of the source. The measurements are interpreted
by means of calculated modeis. P.J.M. Thomeer simplified the interpretation
by characterizing the electrical properties of the subsurface by a wave
number (Thomeer, 1970).
An important improvement came from applying linear filter theory to the
kernel function that appears in the theory of the electromagnetic sounding.
The kernel of an integral equation for the field strength contains the required
information about the layering of the subsurface and the specific resistivity
as a function of depth (Koefoed, Ghosh and Polman, 1972; Verma and Koefoed,
1973). In his thesis R.K. Verma gives a review of electromagnetic methods.
The field around an oscillating magnetic dipole, placed on the earth, is calculated.
The kernel function is subjected to a transformation by means of a digital
linear filter, which means a great acceleration in interpreting the measurements
(Verma, 1973). By the filtering a transform function can be derived from
measurements of resistivity, as a first step in the direct interpretation of data
(Das, Ghosh and Biewinga, 1974).
By combining the electromagnetic method with the electric one, the number
of possible models of conductivity can be greatly reduced . Koefoed and coworkers
applied these methods in 1973 and 1974 in an investigation into the
underground water in the arid areas of South Tunesia (Koefoed and Biewinga.
1976). D. T . Biewinga wrote a report on these experiments (Biewinga, 1977a
122

.. and 1977b) and also a thesis (Biewinga, 1979). The measured conductivity
was compared with values calculated for various modeis. The resolving power
of the electromagnetic soundings appeared to be rat her small.
V. 8.1. Seismological research at the TH of Delft by O. Koefoed and co-workers
Koefoed and co-workers made seismological experiments using reflected and
refracted waves in models of plexiglas (Koefoed, Van Ewijk and Bakker, 1958).
Koefoed calculated the amplitudes of reflected and refracted waves that originate
from the incidence of a longitudinal wave on the boundary bet ween two
media with various elastic parameters and densities (Koefoed, 1962). Together
with his students he studied digital recording of seismic waves, and its deconvolution.
(This is a filtering process for removingunwanted signals as
completely as possible; at the same time, the analysis of the seismogram is
accelerated.) The possibility of increasing the resolving power of seismies by
filtering the signais, was treated by N. de Voogd in his thesis (De Voogd,
1976) and other papers (De Voogd, 1974 and 1978). The increase in resolving
power is attained by deconvolution of the reflected signals by means of digital
filters. Koefoed and De Voogd (1980) applied this technique to the seismie
response of a series of thin coal seams.
V.8.2. Seismological research by A. T. de Hoop and co-workers
A. T . de Hoop was assistent professor of electromagnetic theory at the TH
at Delft from 1953 to 1956. From 1956 to 1957 he was research assistant at the
Institute of Geophysics (Los Angeles, CaUf.). Af ter returning to Delft he became
associate professor at the TH, from 1957 to 1960. From 1960 to the present
he has been professor of electromagnetic theory and applied mathematics
at the TH.
De Hoop became more and more interested in diffraction phenomena, not only
of electromagnetic waves, but also of seismic waves. His work is therefore of
importance for applied geophysics.
He investigated representation theorems for the particle displacement in an
elastic solid, and their application to elastodynamic diffraction theory (Ph. D.
dissertation , De Hoop, 1958). With the aid of these theorems he formulated
the problem of diffraction by an ob st acle , and gave an exact time-domain solution
of diffraction by a semi-infinite rigid baffle and a semi-infinite crack.
A special point in De Hoop 's work was the introduction of a modification of
Cagniard 's method for solving pulsed wave problems (De Hoop, 1960). In order
to give a clear picture of his method, two problems were considered, viz.
the determination of the cylindrical wave generated by an impulsive line source,
and the spherical wave generated by a point source. He showed that the method
could be applied to determine the mot ion generated by any type of point source
located either inside or at the surface of a half-space (De Hoop, 1962). Two
papers on other subjects are: a note on the propagation of waves in a continuously
layered medium (De Hoop, 1964) and a paper on an elastodynamic
reciprocity theorem for linear, viscoelastic media (De Hoop, 1966). The problem
of the pulsed line source at the stress-free boundary of a semi-infinite
elastic soUd ("Lamb's problem") was solved by employing Cagniard-de Hoop's
method (De Hoop, 1970). The pulsed electromagnetic radiation from a line
source in a two-media configuration was investigated using the same method
(De Hoop, 1979).
Some co-workers of A. T . de Hoop also contributed to the solution of diffraction
problems. T.H. Tan investigated the scattering of elastic waves by elastically
123

T
I
M
E
I
N
5
E
C
o
N
D
5
l2t 381 2B8 268 2. Z2e 211 188 168 1.
Figure 53a. A seismie time section obtained from the subsurface of the Netherlands
North Sea shows many reflected and diffracted arrivals. caused by a complex structure
(before migration) .
lZ8 188

transparant obstacles (Tan, 1975a and 1975b). He also studied diffraction of
plane P waves and S waves by an obstacle of finite extent in a homogeneous ,
isotropic, perfectly elastic medium (Tan, 1976a and 1976b). Reciprocity relations
for the scattering of plane, elastic waves were derived (Tan, 1977). Tan
also studied the scattering of plane, elastic waves by a plane crack of finite
width, as weil as the scattering of plane, elastic waves by a plane, rigid strip
(Tan, 1977a and 1977b) .
Scattering of elastic waves was also a matter of interest for F. L. Neerhoff,
co-worker of De Hoop. Neerhoff investigated the scattering of SH waves by
an indentation at the mass-loaded boundary of a semi-infinite elastic medium
(Neerhoff, 1975) and also the scattering and excitation of SH surface waves
by a protrusion at the mass-loaded boundary of an elastic half-space (Neerhoff,
1976). He investigated diffraction of Love waves by a stress-free crack of
finite width in the plane interface of a layered composite (Neerhoff, 1979),
and he formulated reciprocity and power-flow theorems for the scattering of
plane elastic waves in a half-space (Neerhoff, 1980).
Diffraction problems were also treated by J. T. Fokkema and P. M. van den
Berg, co-workers of A.T. de Hoop. J.T. Fokkema pubUshed a paper on diffraction
of elastic waves by the periodic rigid boundary of a semi-infinite soUd
(Fokkema, 1978) and another paper on reflection and transmission of elastic
waves by the spatially periodic interface bet ween two soUds (Fokkema , 1980).
Fokkema and Van den Berg investigated elastodynamic diffraction by a periodic
rough surface (Fokkema and Van den Berg, 1977). They also calculated
the wave motion generated by a time-harmonic buried line source in a soUd
with a stress-free, periodic boundary (Fokkema and Van den Berg, 1980).
V. 8. 3. Research into seismic data processing by A. J. Berkhout and co-workers
An important contribution to exploration geophysics, especially to seismic
data processing, was presented by A.J. Berkhout and co-workers.
Af ter obtaining the degree of physical engineer at the TH at Delft, Berkhout
was a research geophysicist with Shell International Research from 1965 to 1971,
being mainly engaged with seismic data analysis and processing. During 1971
to 1974 he was employed by Brunei Shell Petroleum Co. (Royal Dutch/Shell
Group), developing and applying methods for direct gas and oH detection from
seismic data. In 1975 and 1976 he served as adviser for Shell International
Petroleum Co., on data analysis and processing in seismic exploration . Since
1976 Berkhout has been professor of seismic and acoustics at the University
of Technology at Delft. His main field includes seismic data processing, uit rllsonic
imaging and architectural acoustics .
Whereas before 1960 analyzing seismic reflection records was confined mainly
to finding qualitative correlations bet ween recorded events, digital processing
has become to play an all-important role in exploration seismology since the
early sixties . It became clear that details about subsurface structures and Uthology
could be obtained from seismic data by digital analysis of the records.
Several processing techniques have been developed to improve signal-to-noise
ratio. However, the main problem of an echo-acoustical system is the improvement
of spatial resolution .
Berkhout developed the theory and technique of seismic migration as a tooI
to improve lateral re sol ut ion . Seismic migration has become one of the most
important subjects in seismic research within the last years. The potentialof
seismic migration is far beyond its original objective, i.e. positional correct ion
of records.
Seismic migration is a synthetic focussing technique. It is carried out digi-
126

tally in a processing centre. The wave fields of many sequentially fired shots
are used for one focussed (migrated) depth point. Using the wave equation ,
the recorded data are transformed into a series of new recordings, which represent
simulated recordings at new positions of the recording plane.
It is to Berkhout's credit that he has developed a systems approach to seismic
migration by combining wave theory with discrete inverse filtering methods
(Berkhout , 1978). Together with D. W. van Wulfften Palthe (1979 and 1980)
he introduced migration as a spatial deconvolution process in the space-frequency
domain. A concise review, written by Berkhout (1981), explains wavefield
extrapolation techniques in seismic migration. In the hook "Seismic Migration
, imaging of acoustic energy by wave field extrapolation " Berkhout
(1980) discusses basic theory, different migration techniques and limits of
spatial resolution. The hook is written for all scientists who are dealing with
array methods and imaging techniques in seismics, especially for geophysicists
who want to have an extensive appreciation on methods of wave-equation migration.
A second revised and enlarged edition appeared in 1982.
Berkhout published some papers on the properties of one-sided signais,
with application to seismic signals (1973a, 1973b, 1974). Together with P. R.
Zaanen he studied filtering techniques that are used for deconvolution filtering
(1976, 1977). A method was presented to derive approximate versions of the
wave equation, which allow. finite difference migration for steep dips (Berkhout,
1979). A.J. Berkhout, J. Ridder and L. F. van der Wal (1980) wrote a
treatise on acoustic imaging by wave-field extrapolation . Advanced acoustic
imaging reconstruction techniques combine different echo measurements in
such a way that diffractions collapse, distortions of reflections are corrected
for, and noise is attenuated. W. Crans and A.J. Berkhout (1980) published a
report on the assessment of seismic amplitude anomalies , which may be related
to hydrocarbon pore filling. They showed how a probabilistic assessment depends
on the integration of seismic data, structural and stratigraphic interpretation ,
velocity studies and weIl data.
V. 8. 4. Processing of gravity data at the TH, Delft
Digital filtering can be useful for the analysis of gravity anomalies . This appeared
from a study by B. A. N . C. ApeIl, who designed mathematical filters
for separating local and regional anomalies (Apell, 1974). This filtering means
subtraction of the sliding mean value from the measured data. The problem
of processing gravity data was treated amply in his thesis (Apell, 1979). He
also studied filters for calculating the derivatives of gravity as a function of
depth. This means a transformation of the anomalies from the earth's surface
to a lower level. This also gives a possibility for separating local and regional
anomalies.
V.9. EXPLORATION GEOPHYSICS IN THE STATE UNIVERSITY OF LEIDEN
Research into geophysics in the State University at Leiden was undertaken
by J. G. Hagedoorn, who worked there as extraordinary professor from 1958
to 1977. He dealt mainly with seismic research and with the interpretation of
reflected and refracted waves, caused by explosions. The most important results
of his work were published in the hook "The collected work of J. G .
Hagedoorn", edited by G. Diephuis (1977).
Hagedoorn's thesis (1954) was based on the idea that seismograms caused
127

Berkhout , A. J. (1979) - Steep dip finite-difference migration . Geophys. Prosp.,
27, 197-213.
Berkhout , A. J. and D. W . van Wulfften Palthe (1980) - Migration in the presence
of noise. Geophys. Prosp. , 28, 372-383.
Berkhout , A. J. (1980) - Seismic migration , imaging of acoustic energy by
wave field extrapolation . Elsevier, Amsterdam /North Holland, 1980; 2nd
edition appeared in 1982.
Berkhout, A.J., J. Ridder and L.F. van der Wal (1980) - Acoustic imagingby
wave field extrapolation. Part I: Theoretical considerations, part 11: Practical
aspects. Proc. lOth Intern. Symp. on Acoust. Imaging . Cannes, New
York Plenum Press, 513-565.
Berkhout, A.J. (1981) - Wave field extrapolation techniques in seismic migration
, a tutorial. Geophysics, 46, 1638-1656.
Biewinga, D. T. (1977a) - Electromagnetic depth sounding experiment. Geophys.
Prospect. 25, 13-28.
Biewinga, D. T. (1977b) - A short note about a field test with an elect rom agnetic
frequency sounding instrument. Geoexploration 15, 57-64.
Biewinga, D. T. (1979) - An experiment al study of electromagnetic freq uency
sounding. Proefschrift, Delft.
Bless, M.J.M., P. van Rooyen et al. (1980) - Geophysikalische Untersuchungen
am ast-Rand des Brabanter Massivs in Belgien, den Niederlanden und
der Bundesrepublik Deutschland. Meded. Rijks Geol. Dienst, 32-17, pp.
313-343.
Boeckel, J. J. G. M. van (1968) - Gravitational and geomagnetic investigations
in Surinam and their structural implications. Dissertation , Amsterdam,
1968.
Bosschart, R.A. (1964) - Analytical interpretation of fixed source electromagnetic
prospecting data. Proefschrift, Delft. .
Cambridge, R.A. (1967) - United Nations Special Fund, Surinam Mineral Survey
1961-1965, Final Report. Geol. Mijnb. Dienst van Suriname, Paramaribo.
Crans, W. and A.J. Berkhout (1980) - Assessment of seismic amplitude anomalies.
Oil and Gas Journal, 156-168.
Dalfsen, W. van (1980) - The shallow subsurface temperature field in the Netherlands.
Proc. Second Intern. Seminar on the results of EC Geothermal
Energy Research, Strassbourg, 1980. D. Reidel Publ. Comp., Dordrecht.
Dam, J.C. van (1964) - A simple method for the calculation of standard graphs
to be used in geo-electrical prospecting. Proefschrift, Delft.
Das, U.C., D.P. Ghosh and D.T.Biewinga (1974) - Transformationofdipole
resistivity sounding measurements over layered earth by linear digital
filtering. Geophys. Prospect. 22, 476-489.
Deemter, H. van, and A.W.H. van der Kallen (1978) - Solution of a complex
structural problem by :JD-seismic. 53rd Annual SPE of AIME Fall conf.
preprint no. SPE-7441.
Diephuis, G. (ed. 1977) - The collected works of J.G. Hagedoorn.
129

Dijkstra, J. en A. Volker (1957) - Geo-elektrisch onderzoek op het IJsselmeer.
Rapporten en Mededelingen betreffende de Zuiderzeewerken, No. 6, Dienst
der Zuiderzeewerken.
Eindverslag (1918) - Eindverslag over de onderzoekingen en uitkomsten van
den Dienst der Rijksopsporing van Delfstoffen in Nederland, 1903-1916,
Amsterdam.
Fokkema , J. T. (1978) - Diffraction of elastic waves by the periodic rigid boundary
of a semi-infinite solid. Proc. Roy. Soc. London, A 363, 487-502.
Fokkema, J. T. (1980) - Reflection and transmission of elastic waves by the
spatially periodic interface between two solids. Wave Motion, 2, 375-393.
Fokkema, J.T. and P.M. van den Berg (1977) - Elastodynamic diffraction by
a periodic rough surface (stress-free boundary). Journ. Acoust. Soc.
Am . , 62, 1095-1101.
Fokkema , J. T. and P. M. van den Berg (1980) - Wave motion generated by a
time-harmonic buried line force in asolid with a stress-free periodic boundary.
Journ. Acoust. Soc. Am., 68, 1836-1849.
Gevers, E.C.A. an4 S.W. Watson (1978) - Quantitative interpretation of seismic
data using well logs. 53rd Annual SPE of AIME Fall conf. preprint
no. SPE-7439.
Ghosh, D.P. (1970) - The application of linear filter theory to the direct interpretation
of geoelectric resistivity sounding measurements. Proefschrift,
Delft. Tevens in Geophys. Prospect. 19, 192-217.
Ghosh, D.P. (1971) - Inverse filter coefficients for the computation of apparent
resistivity standard curves for a horizontally stratified earth. Geophys.
Prosp. 19, 769-775.
GMD, Suriname (1971, 1973, 1975) - Mededelingen 21, 22, 23. Contributions
to the Geology of Suriname, Geol. Mijnb. Dienst, Paramaribo.
Groen, D.M. W. te, and W. F. Steenken (1968) - Exploration and Delineation
of the Groningen gas field. Verh. Kon. Ned. Geol. Mijnb. Gen., Geol.
Serie, Vol. 25, 9-20.
Haenel, E. editor (1980) - Atlas of Subsurface Temperatures in the European
Community. Commission of the European Communities, Directorate-General
for Research, Science and Education . Energy Research and Development
Programme , Subprogramme Geothermal Energy.
Hagedoorn, J.G. (1954) - A process of seismic reflection interpretation. Proefschrift,
Utrecht. Ook in Geophys. Prospect. 2, 86-128, 1954.
Hagedoorn, J.G. (1955) - Templates for fitting smooth velocity functions to
seismic refraction and reflection data. Geophys. Prospect. 3, 324-338.
HageEloorn, J.G. (1959) - The plus-minus method of interpreting seismic refraction
sections . Geophys. Prospect. 7, 158-182.
Hagedoorn, J.G. (1962) - In pursuit of the errant seismic pulse. Geophys.
Prospect. 10, 148-165.
Helbig , K. (1980) - Modeling transversely isotropic media by thin isotropic
layers. Prakla-Seismos GMBH.
130

Heybroek, P. (1974) - Tektonische kaart van Nederland. Geol. Mijnbouw 53,
43-50.
Hoeven, F.G. van der (1964) - Interpretation of geoelectric resistivity curves.
Proefschrift, Delft.
Hoogervorst, G. H. T . C. (1976) - Occurrence, elimination , and use of fluctuating
earth-currents. Dissertatie, Leiden.
Hoop, A. T. de (1958) - Representation theorems for the displacement in an
elastic solid and their application to elastodynamic diffraction theory. Thesis,
Delft.
Hoop, A. T. de (1960) - A modification of Cagniard 's method for solving seismic
pulse problems. Appl. Sci. Res., Section B, Vol. 8, 349-356.
Hoop, A. T. de (1962) - Theoretical determination of the surface motion of a
uniform elastic half-space produced by a dilatational, impulsive, point
source. Colloques internationaux du Centre National de la Recherche Scientifique,
no. 111, Marseille, 21-32.
Hoop, A.T. de (1964) - A note on the propagation of waves in a continuously
layered medium. Appl. Sci. Res., Section B, Vol. 12, 74-80.
Hoop, A. T. de (1966) - An elastodynamic reciprocity theorem for linear viscoelastic
media. Appl. Sci. Res., 16, 39-45.
Hoop, A.T. de (1970) - The surface line source problem in elastodynamics.
Elektronika en Telecommunicatie, I, 19-21.
Hoop, A. T. de (1979) - Pulsed electromagnetic radiation from a line source in
a two-media configuration. Radio Science, 14, 253-268.
Huysinga, J.K. and A.R. Biddie (1978) - Shallow seismic as an aid to locating
offshore installations. SPE (UK) Ltd. Europe Offshore Petrol Conf. Proc.
Vol. 2, 425-432.
Jaarverslag (1980) - Dienst Grondwaterverkenning T.N .0.
Koefoed, O. (1955) - Resistivity curves for a conducting layer of finite thickness
embedded in an otherwise homogeneous and less conducting earth.
Geophys. Prospect. 3, 258-267.
Koefoed, 0., J.G. van Ewijk and W. T. Bakker (1958) - Seismic model experiments
concerning reflected refractions. Geophys. Prospect. 6, 382-393.
Koefoed, O. (1962) - Reflection and transmission coefficients for plane longitudinal
waves (compressional). Geophys. Prospect. 10, 304-351.
Koefoed, O. (1965a) - A semi-direct method of interpreting resistivity observations.
Geophys. Prospect. 13, 259-282.
Koefoed, O. (1965b) - Direct method of interpreting resistivity observations.
Geophys. Prospect. 13, 568-591.
Koefoed, O. (1966) - The direct interpretation of resistivity observations
made with a Wenner electrode configuration. Geophys. Prospect. 14, 71-
79.
Koefoed, O. and G. Kegge (1968) - The electrical current pattern induced by
an oscillating magnetic dipole in a semi-infinite thin plate of infinitesimal
resistivity. Geophys. Prospect. 16, 144-158.
131

Koefoed, O. (1968) - The application of the Kernel function in interpreting
geoelectrical resistivity measurements. Borntraeger, Berlin .
Koefoed, O. and A.P. Struyk (1969) - The electrical current pattern induced
by an oscillating magnetic dipole in a semi-infinite thin plate. Geophys.
Prospect. 17, 182-195.
Koefoed, O. (1969) - An analysis of equivalence in resistivity sounding. Geophys.
Prospect. 17, 327-335.
Koefoed, O. (1970) - A fast method for determining the layer distribution from
the raised kernel function in geoelectrical sounding. Geophys. Prospect.
18, 564-570.
Koefoed, 0., D.P. Ghosh and G.J.Polman (1972) - Computation of type curves
for electromagnetic depth sounding with a horizontal transmitting coil by
means of a digital linear filter. Geophys. Prospect. 20, 406-420.
Koefoed, O. (1976a) - Progress in the direct interpretation of resistivity soundings:
an algorithm. Geophys. Prospect. 24, 233-240.
Koefoed, O. (1976b) - An approximate method of resistivity soundirig interpretation.
Geophys. Prospect. 24, 617-632.
Koefoed, O. and D. T . Biewinga (1976) - The application of electromagnetic
frequency sounding to groundwater problems. Geoexploration 14, 229-
241.
Koefoed, O. (1979) - Geosounding Principles 1. Resistivity Sounding Measurements.
Elsevier, Amsterdam.
Koefoed, 0 and N. de Voogd (1980) - The linear properties of thin layers,
with an application to synthetic seismograms over coal seams. Geophysics
45, 1254-1268.
Koefoed, O. (1980) - Collected Papers (1952-1980). University Press, Delft.
Maureau, G. T . F. R. and D. H. van Wijhe (1979) - The prediction of porosity in
the Permian (Zechstein 2) carbonate of eastern Netherlands using seismic
data. Geophysics 44, 1502-1517.
Maureau, G. T . F. R. and D. H. van Wijhe (1980) - The use of advanced seismic
techniques to study carbonate reservoirs. lOth World Petroleum Congress,
Proc. 3, 205-211.
Meetkundige Dienst Rijkswaterstaat (1979) - Rapport over de NAM-waterpassing
van 1978 over het gasveld Groningen. MDNP-R-7908, Delft. Idem
van 1981, MDNP-R-8201, Delft.
Mekel, J.A.A. (1928) - Theorie van het tektonisch-gravimetrisch onderzoek.
Proefschrift, Delft.
Nederlandse Aardolie Maatschappij en Rijks Geologische Dienst (1980) - Stratigraphic
Nomenclature of the Netherlands. Verh. Kon. Ned. Geol. Mijnb.
Gen. 32 .
Neerhoff, F.L. (1975) - Scattering of SH-waves by an irregularity at the massloaded
boundary of a semi-infinite elastic medium. Proc. Roy. Soc. London,
A 342, 237-257.
Neerhoff, F.L. (1976) - Scattering and excitation of SH-surface waves by a
protrusion at the mass-Ioaded boundary of an elastic half-space. Appl.
Sci. Res. 32, 269-282.
132

Neerhoff, F.L. (1979) - Diffraction of Love waves by a stress-free crack of
finite width in the plane interface of a layered composite. Appl. Sci. Res.,
35, 265-315.
Neerhoff, F .L. (1980) - Reciprocity and power-flow theorems for the scattering
of plane elastic waves in a half-space. Wave Motion, 2, 99-113.
Nieuwenkamp, W. (1937) - Electrische opsporing van ertsen in Zuid-Limburg.
Handelingen 26ste Natuur- en Geneeskundig Congres, Utrecht, 1937.
Peelcommissie (1963) - Verslag van de Peelcommissie. Verh. Kon. Ned. Geol.
Mijnbk. Gen., MS 5.
Poley, J. Ph. (1964) - Critical-angle effects in seismic exploration . Geophys.
Prospect. 12, 397-421.
Poley, J. Ph. and J.J. Nootenboom (1966) - Seismic refraction and screening
by high-velocity layers. Geophys. Prospect. 14, 184-203.
Ristow, D. (1980) - 3D-Downward extrapolation of seismic data in particular
by finite difference methods. Thesis, Utrecht.
Sitter, L.U. de, en,medewerkers (1949) - Eindverslag van het geophysische
onderzoek in Z.O.-Nederland (in opdracht van de Geophysische Dienst
der Staatsmijnen). Mededelingen Geologische Stichting, Serie C-I-3, No. 1.
Snijders, G.H.F. (1958) - Reflection shooting techniques in the Netherlands.
Geophys. Prospecting 6, 167-193.
Staal, J.J. and J.D. Robinson (1977) - Permeability profiles from acoustic logging.
52nd Annual SPE of Fall Tech. Conf. Preprint no. SPE-6821.'
Symposium (1979) - Steenkool onder Nederland: Energie voor de toekomst?
- See also: Geol. en Mijnb. , special section, Dec. 1982, Research on coal
beneath the Netherlands , p. 355- 396.
Tan, T. H. (1975a) - Scattering of elastic waves by elastically transparant obstacles.
Appl. Sci. Res., 31, 29-51.
Tan, T. H. (197 5b) - Far-field radiation characteristics of elastic waves and
the elastodynamic radiation condition . Appl. Sci. Res., 31, 363- 375.
Tan, T.H. (1976a) - Theorem on the scattering and the absorption cross section
for scattering of plane, time-harmonic, elastic waves. Journ. Acoust.
Soc. Am., 59, 1265-1267.
Tan, T.H. (1976b) - Diffraction of time-harmonic elastic waves by a cylindrical
obstacle. Appl. Sci. Res., 32, 97-144.
Tan, T. H. (1977) - Reciprocity relations for scattering of plane, elastic waves.
Journ. Acoust. Soc. Am., 61, 928-931.
Tan, T.H. (1977a) - Scattering of plane, elastic waves by a plane crack of
finite with. Appl. Sci. Res., 33, 75-88.
Tan, T.H. (1977b) - Scattering of plane, elastic waves by aplane, rigid strip.
Appl. Sci. Res., 33, 89-100.
Thomeer, P.J.M. (1970) - Analysis of electromagnetic prospecting data by
means of apparent wave numbers. Proefschrift, Delft.
Ulrich, V. P. (1956) - De geophysische opsporing van het olieveld Schoonebeek.
De Ingenieur, 68, no. 32, p. M21, 22.
133

Veldkamp , J. (1951) - Geomagnetic anomalies in the Netherlands. Geologie en
Mijnbouw, 13, 218-223.
Verma, R.K. and O. Koefoed (1973) - A note on the linear filter method of computing
electromagnetic sounding curves. Geophys. Prospect. 21, 70-76.
Verma, R.K. (1973) - A feasibility study of electromagnetic depth sounding
methods. Proefschrift, Delft.
Visser, W. A. (1953) - Olie- en gasexploratie in Nederland. De Ingenieur 65,
No. 33.
Visser, W.A. (1978) - Early subsurface temperature measurements in the Netherlands.
Geol. Mijnbouw, 57, 1-10.
Visser, W. A. (1979) - De mogelijkheden van aardwarmte in Nederland. De
Ingenieur, 91, 804-810.
Visser, W.A . and J.J. Hermes (1962) - Geological results of the exploration
for oil in Netherlantls New Guinea. Verh. Kon. Ned. Geol. Mijnb. Gen.,
Deel XX.
Voogd, N. de (1974) - Wavelet shaping and noise reduction. Geophys. Prospect.
22, 354-369.
Voogd, N. de (1976) - An algorithm for digital Wiener filters and its application
to seismic wavelets in noise. Proefschrift, Delft.
Voogd, N. de (1978) - The phase property of a finite realization of random
noise and its influence on deconvolution. Geophys. Prospect. 26, 509-524.
Weelden, A . . van (1957) - History of gravity observations in the Netherlands.
Verh. Kon. Ned. Geol. Mijnb. Gen., 18 , 305-309.
Wijkerslooth de Weerdesteyn, P. J. C. de (1937) - Geophysikalische Untersuchungen
nach Erzlagerstätten in Süd-Limburg (Holland). Fortschritte der
Mineralogie, Kristallographie und Petrographie, Band. 22.
134

CHAPTER VI
The·teaching of Solid Earth
Geophysics
VI.l. Teaching geophysics at the State University of Utrecht
In the middle of this century lectures in geophysics formed part of the training
of geologists at the Utrecht University. Courses of lectures on gravimetry,
applied geophysics, geomagnetism and seismology were given by F .A. Vening
Meinesz, o. Koefoed and J. Veldkamp . Students of geology could take geophysics
as a second subject in their studies.
Vening Meinesz was appointed extraordinary professor at the Utrecht University
in 1927. There he lectured on cartography and gravimetry, and in the
later years also geotectonics and geophysics (1936-1957). Koefoed taught exploration
geophysics in the years 1947 to 1958. Veldkamp gave lectures on
geomagnetism and seismology (1955-1974).
Af ter World War 11 education in geophysical exploration methods for students
of geology and geophysics had begun in the State University at Utrecht. This
was made possible thanks to the cooperation of Royal Dutch/Shell, who several
times made available a geophysicist for teaehing. Within the framework of
this cooperation Koefoed was assigned to the training of geologists at utrecht
in the years 1947 to 1958.
After Koefoed 's appointment as professor at the TH at Delft, applied geophysics
at the Utrecht University was taught by D.M. W. te Groen from 1959
to 1962, and thereafter by J. Hospers (from 1962 to 1963). After that this lectureship
was replaced by a professorship , which was occupied first by J. C.
d'Arnaud Gerkens from 1965 to 1976, and then by K. Helbig from 1977 to the
present. Geophysical investigations at sea were executed by B. J. Collette. In
1972 he was appointed lecturer and in 1980 professor of marine geophysics.
In the middle of the 1960s geophysics was gradually recognized as an independent
discipline, which might be studied apart from geology. This development
was confirmed by the appointment of J. G. J. Scholte to follow up Vening
Meinesz as a full professor in 1957. Scholte started a training of graduate
students in theoretical geophysics as main subject.
After Scholte 's death (in 1970) N. J. Vlaar was appointed professor of theoretical
geophysics in 1973. He was convinced of the importance of geophysics
within the framework of earth sciences. At the same time the Netherlands industry
and especially the international oil companies showed an increasing demand
for weil trained geophysicists, in connection with the discovery of oil
and gas in north-west Europe.
135

versity of Toronto. There he was successively lecturer and assistent professor
from 1950 to 1960. After having returned to Delft he became professor of
aerodynamics in 1960.
Since 1976 A. J. Berkhout has been professor of seismies and acoustics at
the University of Technology at Delft. He teaches seismie data processing and
ultra-sonic imaging . He has developed a systems approach to seismic migration
by combining wave theory with filtering methods. His book "Seismic migration ,
imaging of acoustic energy by wave field extrapolation " is based on lectures
about theory and migration techniques. His teaching is aimed not only at students
of the TH , but also at geophysicists.
VI. 5. University Teachers of solid earth geophysics
Years Name Location Subiect
1936-1957 F .A. Vening Meinesz Utrecht gravimetry , geodesy,
Delft geotectonics
1947-1958 O. Koefoed Utrecht exploration geophysics
1955-1974 J. Veldkamp Utrecht geomagnetism, seismology
1957-1970 J. G . J. Scholte Utrecht general geophysics
1959-1962 D.M.W. te Groen Utrecht exploration geophysics
1962-1963 J . Hospers Utrecht exploration geophysics
1965-1976 J. C. d 'Arnaud Gerkens Utrecht exploration geophysics
1972-now B . J. Collette Utrecht marine geophysics
1973-now N .J. Vlaar Utrecht theoretical geophysics
1977-now K. Helbig Utrecht exploration geophysics
1939-1962 J. Westerveld Amsterdam geology and mineralogy ,
geophysics
1944-1968 L.P.G. Koning Amsterdam physics, geophysics
1965-1975 J. Hospers Amsterdam general geophysics
1978-now K. Helbig Amsterdam exploration geophysics
1958-1977 J. G. Hagedoorn Leiden exploration geophysics
1929-1940 J .A.A. Mekel Delft geology, exploration
geophysics
1951-1980 O. Koefoed Delft exploration geophysics
1957-now A.T. de Hoop Delft diffraction problems
1950-1960 J. A . Steketee Toronto elasticity theory of dislocations
1976-now A. J. Berkhout Delft seismie and acoustic
data processing
137

digital processing techniques. have enabled investigation into the structure
of conducting layers.
As it can be expected that the development of mathematical and physical
techniques for investigating geophysical problems has not yet reached its peak
but will continue. it can be stated that geophysical research will become more
and more important to man kind .
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