Ground motion and rupture process of the 2003 Tokachi-oki earthquake obtained from strong motion data of K-NET and KiK-net

A great earthquake, named the 2003 Tokachi-oki earthquake, occurred in the southern Kuril subduction zone on 26th September 2003,4:50 JST (41.7797°N, 144.0795°E, 42 km depth; Japan Meteorological Agency). Its ground motion was recoreded at 655 stations of the nationwide strong motion networks, K-NET and KiK-net. A maximum peak ground acceleration of 988 cm/s² (gal) was observed at station HKD100 and amplitudes greater than 200 cm/s² were observed over a wide area of eastern Hokkaido. We used a multi-line linear waveform inversion method to estimate the rupture process from the strong motion data of supplied by 15 stations. We assumed a fault plane model of 140 km × 160 km with strike and dip angles of our fault model are N246°E and 18°, respectively, placed on the estimated upper boundary of the subducting Pacific Plate. The estimated total slip distribution consisted of three major slip areas; (a) around the hypocenter, (b) the northwest part of the fault with the maximum slip of 5.9 m, and (c) the northeast edge of the fault plane. The major asperity (b) was composed of two large slip areas with different slip rate functions: the duration of moment release in the sourtheast part is longer than 15 sec, but in contrast most of the seismic moment of the northwest part was released in a short period of less than 10 sec. Our estimation of the total seismic moment was 2.9 × 10²¹ N·m which corresponded to Mw = 8.2.