Geophysical Abstracts 152 January-March 1953

36 GEOPHYSICAL ABSTRACTS 152, JANUARY-MARCH 1953
14298. Musgrave, Albert W. Wavef ront charts and raypath plotter: Mines Mag.,
v. 43, no. 2, p. 27-31, 54, 1953. :
A seismic ray-path plotter based on a linear increase of velocity with time
has been designed and constructed by Musgrave. Wave-front charts, using
various velocity combinations, may be constructed from the plotter. They are
available from the Colorado School of Mines, Golden, Colo. This paper was
taken from Mr. Musgrave's doctorate thesis which is to be published in the
Colorado School of Mines quarterly in the near future. L. C. P.
OBSERVATIONS OF SEISMIC WAVES
14299. Jeffreys, Harold. The times of P up to 30°: Royal Astron. Soc. Monthly
Notices, Geophys. supp., v. 6, no. 6, p. 348-364, 1952.
Times of P in Mediterranean, Japanese and Californian earthquakes are
analysed with the objects of testing the generality of the increase of the velocity
at short distances found in Europe and the evidence for Gutenberg's layer of low
velocity. The Mediterranean earthquakes do confirm the increase at short dis­
tances, but the Japanese ones agree with the tables in use, and there is clear
evidence of a regional difference. The evidence from North American earth­
quakes is conflicting. It does not definitely indicate any change from the
present travel times, but the uncertainties are larger than in the other regions,
chiefly because there are rarely enough stations in approximately the same
azimuth and at greatly different distances to give much information.
The difference of the times at 2° and 25° is about the same in Europe and
Japan, but in comparison with them the times in Europe at 8° are about 3s
earlier. The time-curve in Europe is nearly linear up to 14°. There is evidence
in both regions for a strong curvature of the time-curve between 15° and 20°, but
it does not decide whether dt/d& is continuous or discontinuous in this interval.
The curvature of the time-curve is in any case surprisingly small, because
laboratory studies of the variation of elastic moduli with pressure indicate an
increase of velocity with depth several times that given by any set of travel
times. Increase of temperature with depth would presumably reduce the rate
of increase but does not appear sufficient to account for the discrepancy.
Author's Abstract
14300. Gutenberg, B[eno]. Wave velocities in the outer part of the earth's
mantle: Nature, v. 170, no. 4320, p. 289, 1952.
Using Mohorovidid's method, the travel times of longitudinal and transverse
waves were computed from the data of about 80 earthquakes with foci at depths
of 20 to 600 km. The values are in good agreement with previous results but give
no evidence of a discontinuity, although supporting the idea of a low-velocity
layer near 100 km. M. C. R.
14301. Di Filippo, D[omenico], and Marcelli, L. Dromocrone per terremoti
vicini e velocita delle onde nell 'Italia Centrale [Travel times for near
earthquakes and the velocity of seismic waves in central Italy]: Annali
Geofisica, v. 5, no. 2, p. 293-310,1952.
From analysis of the seismograms of the strong earthquake of September 5,
1950, which was clearly recorded at more than 30 European seismic observatories,
the travel times of Pn, Pg, P*, Sn, and % were determined. Velocities of these