M 7.3 - 234 km SE of ?funato, Japan

Tectonic Summary

The December 7, 2012, M 7.3 earthquake east of Sendai, Japan, occurred as a result of shallow oblique reverse faulting within the oceanic lithosphere of the Pacific plate, approximately 20 km east of the plate boundary between the Pacific and North America plates that marks the location where the Pacific plate subducts beneath Japan. Focal mechanism solutions indicate that oblique rupture occurred on either a northeast- or southeast-striking, moderately dipping reverse fault. Slip on a fault aligned with either nodal plane is consistent with this intraplate setting. At the epicenter of this earthquake, the Pacific plate moves west-northwestward relative to the North America plate at a velocity of about 83 mm/yr. 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 plate boundary region surrounding the December 7, 2012, earthquake hosts moderate to large earthquakes regularly—12 events of M 7 or larger have occurred within 250 km of this earthquake over the past 40 years. These historic events include the damaging M 9.0 Tohoku earthquake of March 11, 2011, which ruptured a large portion of the subduction zone plate interface to the west of the December 7th event, and which spawned a major tsunami that caused significant devastation along the Honshu Coast. A series of aftershocks of that 2011 megathrust event also occurred to the east of the plate boundary within the Pacific plate, including a M 7.6 normal faulting earthquake 60 km to the northeast of the December 7th event.

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)