M 7.4 - 119 km ESE of Shizunai-furukawach?, Japan

Tectonic Summary

The September 25, 2003, M 7.4 earthquake near Hokkaido, Japan, occurred as the result of shallow thrust faulting on or near the plate interface between the overriding North America plate (which extends into the northeast corner of the Eurasian landmass) and the subducting Pacific plate. It is an aftershock of the M 8.3 earthquake that occurred just over an hour prior and less than 50 km to the west. At the location of the M 7.4 earthquake, the Pacific plate is moving west-northwest at a velocity of about 82 mm/yr relative to the North America plate, subducting beneath Japan and Eurasia at the Japan and Kuril-Kamchatka Trenches to the east of the September 25th earthquake.

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 the subducted Pacific plate. The earthquakes of March 4, 1952, and May 16, 1968, were interface-thrust earthquakes, whereas the M 7.6 earthquake of January 15, 1993 occurred within the interior of the subducted Pacific plate. The 1993 event resulted in at least 2 fatalities and more than 900 injured. The September 25th earthquake appears to have involved rupture of the same section of the plate interface that ruptured in 1952.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)