A feasibility test of CMT inversion using regional network of broad-band strong-motion seismographs for near-distance large earthquakes

When a large earthquake occurs in and around the Japanese Islands, we should immediately determine the size and the fault geometry of the earthquake to mitigate earthquake disasters. Broad-band, strong-motion data of near-distance large earthquakes are used to investigate the possibility of CMT inversion. We perform a moment tensor inversion using the data sets of the 1993 Hokkaido Nansei-oki earthquake (MJMA 7.8), the 1994 Hokkaido Toho-oki earthquake (MJMA 8.1) and the 1994 Sanriku Haruka-oki earthquake (MJMA 7.5). The accuracy of the solutions is examined by comparison with the solutions derived from global data sets, which reveals that the mechanism and moment magnitude are quite adequate for the purpose. Numerical experiments are made to analyze the influence of the source finiteness on the solutions. The numerical experiments suggest that the influence of the source finiteness on the mechanism retrieval is smaller than that on the moment retrieval. We suggest the installation of a network system of broad-band, strong-motion seismographs in the Japanese Islands.