The preliminary location and focal-mechanism of this earthquake imply that it occurred as the result of thrust-faulting on the plate interface between the overriding North American plate (which extends into the northeast corner of the Eurasian landmass) and the subducting Pacific plate.
The Pacific plate is moving west-northwest at a rate of about 8.2 cm per year relative to the North American plate. In addition to experiencing great thrust earthquakes that originate on the interface between the plates, eastern Hokkaido experiences great earthquakes that originate from the interior of subducted Pacific plate. The earthquakes of 4 March 1952, and 16 May 1968 were interface-thrust earthquakes, whereas the earthquake of 15 January 1993 occurred within the interior of the subducted Pacific plate. The 25 September earthquake appears to have involved rupture of the same section of the plate interface that ruptured in 1952.
The last great earthquake (magnitude 8 or greater) in the world was a magnitude 8.4 that occurred on 23 June 2001, near the coast of Peru. This earthquake killed at least 75, including 26 killed by the associated tsunami.
PREVIOUS DEADLY EARTHQUAKES IN THIS REGION
4 March 1952 31 killed, 72 injured; 713 houses destroyed, 5,980 damaged. 28 killed and warehouses destroyed at Kushiro. 3 killed and 309 houses destroyed at Kiratapu. 1,000 houses destroyed or damaged at Shiranuka and 400 schools collapsed at Sapporo. 10-foot tsunami.
16 May 1968 Damage estimated at 25 million USD.
15 January 1993 614 injured and substantial damage (VI JMA) at Kushiro, Hokkaido and Hachinohe, Honshu. Felt (V JMA) at Hiroo, Nemuro, Obihiro, Otaru and Urakawa; (IV JMA) at Hakodate and Tomakomai; (III JMA) at Sapporo, Hokkaido. Felt (IV JMA) at Aomori and Morioka; (III JMA) at Akita, Fukushima, Sendai, Tokyo and Yokohama, Honshu. Also felt (VII) on Shikotan and (VI) at Kurilsk, Kuril Islands. Landslides and subsidence occurred in the epicentral area.