抄録
There are six subcrustal earthquake nests (seismically active regions) of sizes of about 20km in the south Kanto district, central Japan. Magnitudes of interplate seismic couplings between the Eurasia, the Pacific and the Philippine Sea plates descending below the south Kanto district have been estimated at these nests.
There was one event (called a master event) of magnitude of about 6.0 or smaller at each earthquake nest, for which the previously published estimate of the scalar seismic moment by the waveform analysis or moment tensor inversion was used. Scalar seismic moments of smaller events have been inferred by Rayleigh wave amplitude relative to those of corresponding master event on vertical component records of five WWSSN stations within about 30° epicentral distance. The interplate seismic coupling at each nest has been obtained as a ratio of accumulated seismic moment to that predicted by relative plate motion models. Thus determined magnitudes of the interplate seismic coupling are 0.1-0.2, comparable to those at continental slope area between the Japan Islands and the Japan trench.
Above estimate suggests a potential ability of brittle fracturing along the interplate boundary between the Philippine Sea and the Eurasia plates at 30-50km depths directly below the Metropolitan Tokyo, in the middle of the south Kanto district. This raises a new possibility on a hypocenter location of the recurrent Tokyo earthquakes, which periodically destroyed the Metropolitan Tokyo once about one hundred years in historic times.
