M 7.3 - 120 km SE of ?funato, Japan

Tectonic Summary

The March 9, 2011, M 7.3 earthquake near the east coast of Honshu, Japan, occurred as a result of shallow thrust faulting on or near the subduction zone interface plate boundary between the Pacific and North America plates. At the location of this earthquake, the Pacific plate moves approximately westward relative to the North America plate at a velocity of 83 mm/yr. The Pacific plate thrusts underneath Japan at the Japan Trench, east of the March 9th earthquake, and dips to the west beneath Eurasia. The location, depth, focal mechanism solutions, and finite-fault modeling of globally distributed seismic data for the March 9th earthquake are consistent with the event resulting from thrust faulting associated with subduction along this plate boundary. Note that some authors divide this region into several microplates that together define the relative motions between the larger Pacific, North America and Eurasia plates; these include the Okhotsk and Amur microplates that are part of North America and Eurasia, respectively.

The Japan Trench subduction zone has hosted nine events of M 7+ since 1973. The largest of these was a M 7.8 earthquake approximately 230 km to the north of the March 9th event, in December 1994, which caused 3 fatalities and almost 700 injuries. In June 1978, a M 7.7 earthquake 75 km to the southwest caused 22 fatalities and more than 400 injuries. In December 2008, a sequence of four moderate earthquakes (M 5.3–5.8) occurred within 20 km of the March 9th event. In the first 12 hours following the March 9th earthquake, the region has experienced more than a dozen aftershocks of M 5+, the largest being M 5.7.

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)