A study of the relation between the periods of elastic waves and the distance traveled by them, based upon the seismographic records of the California earthquake, January 31, 1922
The epicenter of the earthquake of January 31, 1922, was found to be approximately the point whose coördinates are 41°8′±3′N, 125°30′±3′W. The time of occurrence was determined as 13h. 17m. 21s.±1s. M.G.C.T. The arrival times of the preliminary phases at the Pacific Coast stations followed approximately Gutenberg's 1914 curve, not Angenheister's 1921 curve for deep-sea paths. The arrival times of the L group and of the M group of waves at trans-Pacific stations agreed in a qualitative way with the observations of Tams (41) and of Angenheister (3), showing greater speed under the Pacific Ocean that under the American continent. Still, the agreement could not be said to be quantitative. Neither did L agree with M in speed change for the same stations. The period of a long wave at the beginning of P was found to decrease and that of a very short, superposed wave to increase with distance from the epicenter. There seemed to be no functional relation between the periods of S waves and the epicentral distances. The periods of two maxima, the one two minutes and the other four minutes after the beginning of the M group of waves, showed a rapid increase with distance from the epicenter. It is possible to represent the observed increase in the first quadrant as a linear function of either the travel time or the epicentral distance. The periods of the same two maxima at Batavia, which furnished the only reliable observation in the second quadrant, while not decisive, would seem to suggest that the linear function is only a first approximation. The form of the function in the second quadrant remains for future study.