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Radiation mode of S waves from a deep-focus earthquake as derived from observations

DOMINION OBSERVATORY, OTTAWA, Canada

Abstract

Two representative hypotheses on earthquake mechanism (so-called force types I and II) have been examined in comparison with seismograms for the earthquake of February 18, 1956 (south off Honshu, Japan; h = 450 km). On the basis of the fault-plane solution derived from P-wave data, one can predict polarity and relative amplitude of shear wave phases for a given station. The prediction by both of the hypotheses is compared with the observations at Kiruna and several other stations, where the principal seismic phases have been recorded clearly.

The comparison has proved that the force type I does not fit the present case. The second type, on the other hand, explains the observations more consistently, although there are minor disagreements with respect to later phases.

Reduction of the recorded wave form by an analog computer has shown that the original seismic disturbance (S) from the source is very simple in its wave form and harmonizes very well with Honda's theory. If we accept his theory, the radius of the origin sphere is estimated at 30-40 km for the present case.

Footnotes

(On Leave from Earthquake Research Institute, University of Tokyo, Tokyo, Japan)

This article has been cited by other articles:

				T. HIRASAWA and W. STAUDER Spectral analysis of body waves from the earthquake of February 18, 1956 Bulletin of the Seismological Society of America, December 1, 1964; 54(6A): 2017 - 2035. [Abstract] [PDF]