Magnitude of deep-focus earthquakes in and near japan

Abstract

The writer tried to obtain the same M as those given by the Pasadena seismological laboratory for the deep-focus earthquakes in and near Japan by using the seismological data obtained at Japanese stations. And the writer succeeded in finding a method to get M with a difference of + 0.3 unit of magnitude as compared with the Pasadena determination. It is shown that the calculated log A/T-Δ curves for deep earthquakes of various depths on the basis of Norman Ricker1891's wavelet theory fit well with the observed values. It is shown that the magnitude of deep earthquakes can be given by the formula, 0.63M= log A0/T0+α (H), so far as the magnitude does not exceed 7. If M exceeds 7, we must use the other formula, { 0.63 + 0.08 (log A0/T0+α (H) -4.4) } M=log A0/T0+α (H). And α (H) is given by the formula α (H) =2.5 log t0 - 2.8, where to is the travel time of the S phase at the epicenter. It is shown that the station corrections for dee p earthquakes are quite different from those for shallow earthquakes. Some examples are shown to sugges t that there is the azimuthal factor among the observed log A/T, having some intimate connections with the mechanism of the occurrence of the earthquakes. Some theoretical considerations are made o n the formula log A0/T0 =0.63M-α (H). © 1959, Japan Meteorological Agency. All rights reserved.