Abstract
The 1969 and 1975 great Kurile earthquakes occurred along the Kurile trench. Tsunamis generated by these earthquakes were observed at tide gauge stations around the coasts of the Okhotsk Sea and Pacific Ocean. To understand rupture process of the 1969 and 1975 earthquakes, slip distributions of the 1969 and 1975 events were estimated using tsunami waveform inversion technique. Seismic moments estimated from slip distributions of the 1969 and 1975 earthquakes were 1.1 × 1021 Nm (Mw 8.0) and 0.6 × 1021 Nm (Mw 7.8), respectively. The 1973 Nemuro-Oki earthquake occurred at the plate interface adjacent to that ruptured by the 1969 Kurile earthquake. The 1975 Shikotan earthquake occurred in a shallow region of the plate interface where was not ruptured by the 1969 Kurile earthquake. Further, like a sequence of the 1969 and 1975 earthquakes, it is possible that a great earthquake may occur in a shallow part of the plate interface a few years after a great earthquake that occurs in a deeper part of the same region along the trench.
Highlights
An interplate earthquake occurred off east Hokkaido, Japan, on August 12, 1969 (Fig. 1)
The 1975 Shikotan earthquake occurred at a shallow part of the plate interface, after the 1969 earthquake which occurred at a deeper part of the same region (Fig. 1)
The slip distribution and calculated errors of the slip amount on each subfault of the 1969 great Kurile earthquake are shown in Fig. 2a and Table 2
Summary
An interplate earthquake occurred off east Hokkaido, Japan, on August 12, 1969 (Fig. 1). Abe (1973) estimated the earthquake mechanism of a pure thrust type and the seismic moment of 2.2 9 1021 Nm (Mw 8.2) using surface waves. The 1975 Shikotan earthquake occurred at a shallow part of the plate interface, after the 1969 earthquake which occurred at a deeper part of the same region (Fig. 1). The 1975 earthquake was characterized as a tsunami earthquake (Takahashi 2006) as the tsunami wave is much larger than that expected from short-period seismic waves. Takemura et al (1977) estimated a seismic moment of 2.0 - 3.0 9 1020 Nm (Mw 7.5–7.6) using surface wave data of the 1975 earthquake. Sasatani and Kasahara (1978) estimated a seismic moment of 5.0 9 1020 Nm (Mw 7.7) using body wave data of the 1975 earthquake.
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