The October 25, 2013 M 7.1 earthquake offshore of Honshu, Japan occurred as the result of normal faulting in the shallow oceanic crust of the Pacific plate. The earthquake occurred outboard (east) of the Japan Trench, which marks the seafloor expression of the subduction zone plate boundary between the Pacific and North America plates, which is immediately up-dip of the source region of the March 2011 M 9.0 Tohoku earthquake. At the latitude of this earthquake, the Pacific plate moves westwards with respect to the North America plate at the rate of 83 mm/yr before subducting beneath the island of Honshu.
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 respectively part of North America and Eurasia. The location, depth, and focal mechanism of the October 25 2013 event are consistent with normal faulting rupture near the outer-arc high of the Japan Trench. In this region, normal faulting is encouraged by both the bending of the Pacific plate as it enters the subduction zone, and by stresses transferred from the locked subduction thrust interface to the west.
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