2001 Volume 53 Issue 4 Pages 373-384
Long-term seismicity change in and around Shizuoka City is investigated on the basis of seismic observation records at the Shizuoka Local Meteorological Observatory (SLMO). Distance of small earthquakes from SLMO is evaluated by S-P times. Since the start of observation in Jan. 1941, almost all earthquakes with M 3 or larger are estimated to have been reported. It is found that long-term seismicity on the western coast of Suruga Bay has changed substantially several times: It was active in 1940s and became low noticeably after mid 1960s. We show that the decrease of seismicity after mid 1960s can not be regarded as an artifical one, but is real. Interesting facts are that seismicity near Shizuoka city was very quiet during about one year just before the 1944 Tonankai earthquake and many induced earthquakes occurred in the area around SLMO after the event.
