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Tectonic Summary

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 Okhotsk plate and the subducting Pacific plate. The Pacific plate is moving northwest at a rate of about 8 cm per year relative to the Okhotsk plate. The Pacific plate begins its decent into the mantle at the Kuril trench that lies about 160 km to the southeast of the earthquake. At first, the plate subducts at an extremely low angle than when it reaches a depth of about 30 km the angle of subduction steepens to about 30 degrees.

In addition to experiencing significant 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 Setember 25, 2003, March 4, 1952, and May 16, 1968 (cited below) were interface-thrust earthquakes, whereas the earthquake of January 15, 1993 (cited below) occurred within the interior of the subducted Pacific plate.

Previous Noteworthy Earthquakes in this Region

2003 September 25, Magnitude 8.3
At least 589 people injured, extensive damage, landslides and power outages occurred and many roads damaged in southeastern Hokkaido. A tsunami generated with an estimated wave height of 4.0 meters along the southeastern coast of Hokkaido. Felt strongly in much of Hokkaido. Also felt in northern and much of central Honshu as far south as Tokyo.

1993 January 15, Magnitude 7.6

2 killed. 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.

1968 May 16, Magnitude 7.9

48 killed. Damage estimate at 25 million USD.

1952 March 4, Magnitude 8.1

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.