Recurrence of Recent Large Earthquakes Along the Southernmost Kurile‐Kamchatka Subduction Zone

Recurrent large earthquakes in the southernmost part of the Kurile-Kamchatka subduction zone were studied. Previous studies have indicated that the 1994 Sanriku-oki earthquake (Mw 7.8) ruptured only the southern part of the rupture area of the 1968 Tokachi-oki earthquake (Mw 8.2), and left the main rupture interface of the 1968 earthquake intact. Also, the 2003 Tokachi-oki earthquake (Mw 8.1) did not rupture the eastern part of the rupture area of the 1952 Tokachi-oki earthquake (Mw 8.2). The rupture processes of the 1973 and 1894 Nemuro-oki earthquakes were studied through tsunami waveform analyses. The rupture of the 1973 Nemuro-oki earthquake was concentrated on the plate interface off Nemuro, Hokkaido, and the seismic moment was estimated to be 6.5 x 10 20 Nm (Mw 7.8). The 1894 Nemuro-oki earthquake ruptured much larger area than that of the 1973 Nemuro-oki earthquake. The fault length of the 1894 earthquake was about 200 km, and the seismic moment was 28.8 x 10 20 Nm (Mw 8.3). In this subduction zone, none of three sets of recent recurrent large earthquakes, the 1968 Tokachi and 1994 Sanriku-oki earthquakes, the 1952 and 2003 Tokachi-oki earthquakes, and the 1894 and 1973 Nemuro-oki earthquakes, have the same rupture processes. Variable rupture patterns of large recurrent earthquakes make it difficult to estimate the source processes of future large earthquakes in this subduction zone. These non-regular recurrences also suggest that, in addition to invariant geometric and material heterogeneities, the dynamic stress heterogeneities are seen to be important for understanding large earthquake complexity in this subduction zone.