EurOCEAN 2000 - Vlaams Instituut voor de Zee

Applications of 3-Dimensional Electromagnetic Induction
by Sources in the Ocean
7. ISO-3D
MARTIN C. SINHA 1 , AGUSTA H. FLOSADOTTIR 2 ,
ANDREAS JUNGE 3 , J. MIGUEL A. MIRANDA 4
1 Southampton Oceanography Centre, University of Southampton, United Kingdom; 2
Laboratory of Oceanic and Atmospheric Sciences, Halo Ltd., Reykjavik, Iceland; 3 Institut für
Meteorologie und Geophysik, Johann Wolfgang Goethe-Universität Frankfurt am Main,
Germany; 4 Centro de Geofisica, Instituto de Ciencias da Terra e do Espaço, Universidade de
Lisboa, Portugal
1. INTRODUCTION
In the field of marine geoelectromagnetism, two important emerging technologies are leading
to new opportunities for studying the properties of, and processes occurring within, both the
ocean itself and the solid earth beneath it. Both of these technologies involve the measurement,
for either geophysical or oceanographic purposes, of electric or magnetic fields induced in the
ocean and the underlying earth by electromagnetic sources within the water column. The
sources may be either natural or artificial. The two relevant technologies are controlled source
electromagnetic sounding, and techniques for measuring naturally induced electromagnetic
fields on the seafloor using ocean bottom instruments and telecommunications cables. ISO-3D
is aimed at improving the exploitation of both of these techniques, and developing theoretical and
experimental methods for making more effective use of observations of electric and magnetic
fields in the oceans induced by both artificial and natural sources. The project is focused in
particular on the extension of existing methodologies to take account of fully 3-dimensional
induction geometries.
At the core of the ISO-3D project is the development of a computer modelling code able to predict
the induced electric and magnetic fields from an arbitrary electromagnetic source, embedded in a
structure in which the electrical properties of the ocean and the solid earth are allowed to vary in
three dimensions. The project has developed this code, and is now exploiting it firstly in a series
of numerical modelling studies; and secondly in a demonstration 3-D controlled source
electromagnetic (CSEM) sounding experiment on the ocean floor. The target of the CSEM survey
is the Lucky Strike segment of the Mid-Atlantic Ridge (SW of the Azores), where the upper
oceanic crust is penetrated by a vigourous, high-temperature hydrothermal circulation system, and
where constraints from the CSEM experiment on the porosity and temperature structure of the
crust are leading to improved understanding of the physical processes associated with high
temperature hydrothermal fluxes between the lithosphere and hydrosphere.
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