明治の東京地震 (1894年) の震源パラメーターについて

Old seismograms of the Tokyo earthquake in the Meiji era (June 20, 1894) were analyzed to retrieve source parameters. This earthquake gave considerable damage on the Tokyo metropolitan area. The focal depth was estimated to be about 50km or about 80km from S-P times of several seismograms observed at Tokyo. The magnitude, which was calculated from data of maximum amplitudes, was 6.6. The focal mechanism and the seismic moment were inferred from waveform fitting with seismograms observed by a Ewing-type strong motion seismograph and a Gray-Milne-Ewing-type seismograph. The estimated moment is 1-3×10¹⁸Nm (M_w=6.0-6.3). The earthquake is considered to have a nearly vertical nodal plane with N-S strike, and to have occurred in the Pacific plate or the Philippine Sea plate. Stress drop of the event was larger than the average value in the region.