High resolution relative hypocenters of similar earthquakes by cross-spectral analysis method

Abstract

Temporal seismic observation at Kamikuga (KKG) in Tochigi Prefecture was carried out from December 18, 1982 to February 11, 1983. Four temporal stations have been installed and more than 300 seismic events have been observed. Cross-spectral analysis method (CSAM) are applied for the precise determination of relative hypocenters of microearthquakes. An earthquake swarm, which consists of events with very similar waveforms, was analyzed by CSAM. For some groups of similar earthquakes, it has been demonstrated that relative hypocenters are determined, with an accuracy of about 50 m. We found two kinds of such groups of similar earthquakes. The first kind is characterized by similar earthquakes, occurring in a very short time interval within a very small area. Characteristic separation among the hypocenters of similar events is smaller than a wavelength of P-waves. The second kind is characterized by similar events occurring rather intermittently in a region with a linear dimension much larger than the wavelength. Although the former would correspond to stick-slip similar events studied by many seismologists, the latter will be similar events controlled by frequency characteristics of propagation paths. © 1985, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan. All rights reserved.