On the Travel Time of Earthquake Waves. (Part II)

[摘要] In the previous report, time-distance curves of P-wave are obtained by some large earthquakes of both shallow and deep origins occured in our country. Then the “Japanese mean time-distance curve of P” is determined and discussed comparing with other some curves which were already obtained by foreign authors. In the present report, the time-distance curve of S-wave is obtained by the large deepfocus earthquake of Mar. 29, 1928, and its “reduced time-distance curve” is also made. It is generally known that a distinct phase of S is sometimes very difficult to find in the seismograms observed in the case of shallow earthquake. In the present investigation, it is found to be still difficult to get an accurate time-distance curve even by the earthquake (1930, V. 24) having the focal depth of 85 km.From two time-distance curves of P and S, the propagating velocities of seismic waves in the earth crust are calculated by well-known Herglotz and Wiechert's method. The result thus obtained may be seen in the tables as well as the illustrations shown in the following part written in Japanese. These values obtained by us are nearly similar to those of E. Wiechert, B. Galitzin, C. G. Knott and others, especially to those of H. Witte which were deduced from the time-distance curves recently obtained by H. Jeffreys. Indeed, this investigation is nothing but a usual calculation sometimes tried by seismologists, but our present result is considered to be worthy of notice on the point of accuracy.

[学科分类] 大气科学