VARIATIONS OF THE TIDAL COMPONENT IN HIGH FREQUENCY SEISMIC NOISE ARISING FROM CHANGES IN EARTH STRESSES

Abstract

This study is concerned with the response of high frequency seismic noise (HFSN) to earth tide, namely, to one of its components, the tidal wave O1 (of period 25.8 hours), which is taken to be a reference effect. Three-year observations of HFSN in Kamchatka were studied to discover that the HFSN component of period 25.8 hours involves a time-varying phase, the variation being related to changes in the state of stress in the earth. Seismicity was examined within 250 km from the recording site. Eight magnitude 6 or greater earthquakes were preceded by a stabilization of the phase at some level during 1 to 3 months and an abrupt change after the earthquakes.