本州中部のテクトニクスと1993年の静岡の地震

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The Crustal Activity Observatory of Shizuoka University has been carrying out seismological observations since 1979. This report describes the results of the seismological observations since 1990,especially on the earthquakes in Shizuoka on 7-11 August 1993,which had a maximum magnitude of 4.2,and their relation to the tectonics of central Japan. The differences in magnitude (ΔM) between Shizuoka University and the Japan Meteorological Agency for 858 earthquakes with an epicenter less than 200 km from the observatory and with a focal depth shallower than 200 km have been examined, and the systematic differences with the focal azimuths are found. The relation between the magnitude and duration of the earthquakes is determined, based on seismological observations from June to August 1993. The foci of the earthquakes in Shizuoka in August 1993 were located on the Kusanagi Fault, and the changes in the ratios of the maximum amplitudes of P and S waves were observed during the earthquakes. The dislocation along the Kusanagi Fault is tilting the Udo Hills about 10°northwestward, and the rate of uplift of the Udo Hills is 4 mm/yr. The Kusanagi Fault is characterized by the landward boundary of a fore-arc basin along the subductive boundary of the Philippine Sea Plate and gravitational collapse. The seismic activities in central Japan are related to the bending of the zonal stucture and collision of the Izu Arc, caused by the motion of the Philippine Sea Plate. Historically, large earthquakes in Shizuoka, Southwest Japan, the northern Fossa Magna, Niigata, Misaka, the Matsuzaki Uplift Zones, and the Zenisu Ridge have happened closely in a time series.

本州中部のテクトニクスと1993年の静岡の地震

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