Slip distribution of the 1952 Tokachi‐Oki earthquake (<i>M</i> 8.1) along the Kuril Trench deduced from tsunami waveform inversion

Abstract

We inverted 13 tsunami waveforms recorded in Japan to estimate the slip distribution of the 1952 Tokachi‐Oki earthquake ( M 8.1), which occurred southeast off Hokkaido along the southern Kuril subduction zone. The previously estimated source area determined from tsunami travel times [ Hatori , 1973 ] did not coincide with the observed aftershock distribution. Our results show that a large amount of slip occurred in the aftershock area east of Hatori's tsunami source area, suggesting that a portion of the interplate thrust near the trench was ruptured by the main shock. We also found more than 5 m of slip along the deeper part of the seismogenic interface, just below the central part of Hatori's tsunami source area. This region, which also has the largest stress drop during the main shock, had few aftershocks. Large tsunami heights on the eastern Hokkaido coast are better explained by the heterogeneous slip model than previous uniform‐slip fault models. The total seismic moment is estimated to be 1.87 × 10 21 N m, giving a moment magnitude of M w = 8.1. The revised tsunami source area is estimated to be 25.2 × 10 3 km 2 , ∼3 times larger than the previous tsunami source area. Out of four large earthquakes with M ∼ 7 that subsequently occurred in and around the rupture area of the 1952 event, three were at the edges of regions with relatively small amount of slip. We also found that a subducted seamount near the edge of the rupture area possibly impeded slip along the plate interface.