T31C-4610:
Source process of large (M~7) earthquakes in Japan Sea estimated from seismic waveforms and tsunami simulations
Abstract:
Inversion of teleseismic waveforms yielded fault parameters of four M~7 earthquakes occurred between 1963 and 1983 in Japan Sea. Tsunami waveforms were simulated based on those parameters and compared to the observed waveforms on tide gauges.Eastern margin of Japan Sea has been considered as a nascent plate boundary between the Eurasian and North American plates but not a typical subduction zone, hence the maximum magnitude (M<8) of earthquakes is smaller than those in the Pacific Ocean. Nevertheless, several large earthquakes with M > 7.5 in the last century caused seismic and tsunami damages, such as the 2007 Chuetsu-oki (Mw 6.6), 2007 Noto (Mw 6.7), 1993 South off Hokkaido (Mw 7.7), 1983 Japan Sea (Mw 7.7), 1964 Niigata (Ms 7.5), or 1940 Shakotan-oki (Mw 7.5) earthquakes. Detailed studies of source process were performed for these earthquakes. Smaller (M~7) earthquakes also cause seismic and tsunami damages if their hypocenters are near the land. However, there are few analyses for earthquakes around M7. Therefore, we study the characteristics of the M~7 earthquakes in Japan Sea.
The earthquakes we studied are the 1983 West off Aomori (MJMA 7.1), 1971 West off Sakhalin (MJMA 6.9), 1964 off Oga peninsula (MJMA 6.9), and 1963 Offshore Cape Echizen (MJMA 6.9) earthquakes. From the teleseismic waveforms inversions, the reverse-fault mechanisms were obtained except for the 1963 earthquake which has the strike-slip-fault mechanism. The fault area is 900 km2, 2800 km2, 3600 km2, and 3600 km2, respectively. Tsunami numerical computations are made from the source models obtained by the teleseismic inversions. Tsunamis from the 1983 earthquake were recorded at 32 tide gauge stations along the Japan Sea. Amplitudes of the calculated tsunami waveforms are much smaller than the observations. For the 1971 earthquake, amplitudes of the calculated tsunami waveforms are also smaller than the observations at 18 tide gauge stations. For the 1964 earthquake, the amplitudes are similar but the waveforms are very different from the observations at 15 tide gauges.