Slip history of the 1994 Sanriku-Haruka-Oki, Japan, earthquake deduced from strong-motion data

Abstract We analyzed the seismic waves of the 1994 Sanriku-Haruka-Oki earthquake (Mw = 7.7), which occurred in the aftershock area of the 1968 Tokachi-Oki earthquake (Mw = 8.2). Applying a multiple-time window inversion scheme to near-source strong-motion data, we obtained a detailed spatiotemporal rupture process and compared it with that of the Tokachi-Oki earthquake. The fault geometry is constructed based on the aftershock distribution. The obtained rupture model is consistent with the CMT solution even for a non-double-couple component. The total seismic moment is 4.0 × 1020 N-m. Large slips are concentrated in three asperities: the first asperity centers about 40 km south and 50 km west from the hypocenter with a maximum slip of 4.4 m, the second one centers about 60 km west from the hypocenter with a maximum slip of 2.2 m, and the third one lies about 110 km west from the hypocenter with a maximum slip of 2.6 m. The obtained moment rate and the duration on the first and second asperities are lower and much longer than those on the third asperity, respectively. The first asperity does not overlap with an area of large slip during the Tokachi-Oki earthquake, but the second or third seem to overlap with or be adjacent to the asperity of the Tokachi-Oki earthquake. Our inversion result also shows an abrupt change of the rupture velocity (from 1.8 to 3.0 km/sec) at the central part of the fault plane. A difference of the seismic coupling between the oceanic and the continental lithospheres at the trenchward side and at the landward side of the 143° E meridian seems to affect the rupture process of this earthquake.