Poster of the Ryukyu Islands, Japan Earthquake of 26 February 2010 - Magnitude 7.0

Tectonic Summary

The Ryukyu Islands earthquake of February 26, 2010, occurred near the boundary that accommodates most of the relative motion between the Philippine Sea and Eurasia tectonic plates. In the region of the earthquake, the Philippine Sea plate moves WNW with respect to the interior of the Eurasia plate, with a relative velocity of approximately 60 mm/yr. The Philippine Sea plate subducts beneath the Eurasia plate at the Ryukyu Trench and is seismically active to depths of about 250 km. The initial estimates of the earthquake's epicenter, focal-depth, and focal-mechanism imply that the shock occurred as an intraplate event either within the subducting Philippine Sea Plate, or within the overlying Eurasia plate, rather than on the thrust-fault plate interface that separates the two, but preliminarily data do not clearly discriminate between these two possibilities.

The largest, instrumentally recorded, shallow-focus, earthquakes from the region of the central Ryukyu trench have had magnitudes in the 7.1 7.4 range.

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