日本列島近辺のサイレントアースクエーク検出の試み

抄録

This is a preliminary report on an attempt to detect silent and slow earthquakes that are supposed to occur around Japan Islands between the Eurasian and the subducting Pacific plates, where inter-plate seismic coupling is 0.2-0.3. In the first step, we have obtained high-pass filtered strain with a cut-off period of 7 hours from the quartz-pipe extensometer records (sampling interval is 5min) of Matsushiro Seismological Observatory of Japan Meteorological Agency for a period from July 1988 to November 1989. When we have found a signal of a pulse width of -10min to -1 hour above a noise level of 10-9 in the high-pass filtered strain, we have calculated spectrum by the Maximum Entropy Method of the quartz-pipe extensometer seismograms (sampling interval is 0.2s) of an 48 hour length. For days when eigenperiods of Earth's free oscillations have been found in the spectrum by the Maximum Entropy Method, we have calculated Sompi-spectrum of IDA long period records, where we could not identify any eigenperiods of spheroidal oscillations of periods longer than 500s. We thus could not find silent and slow earthquakes for the period around Japan Islands with the above tactics.