Periods of the Ground in Southern California Earthquakes

Abstract

From the early seismic records various Japanese scientists found that the microseisms which are produced by traffic, industry, and meteorological conditions, as storms and surf, show certain prevailing periods which are different in different localities. Omori and Kikuchi have especially investigated this problem. Kikuchi expressed his opinion that the prevailing periods constituted the free periods of the ground and their harmonics. The problem of the connection between periods of microseisms produced by local causes and the free periods of the ground has been investigated frequently since. O. Geussenhainer in his investigation of microseisms in Göttingen with periods between 5 and 9 seconds found that they change gradually in the course of time in the vertical component, but that in the horizontal component periods of 6, 7.5, and 9 seconds prevail. He believed these periods to be free periods of Love waves in the ground near Göttingen or harmonics of such.