Earthquake Offshore Northwest of the Okinawa Main Island on May 21

On May 21, 2012 at 12:18 (JST), there was a M5.1 earthquake (maximum seismic intensity 3) at a depth of 91 km, offshore northwest of the Okinawa Main Island. This event occurred within the Philippine Sea plate. The focal mechanism (CMT solution) had a compression axis in an NNW-SSE direction.
For the seismic activity since October 1997, in the vicinity of the recent event (Area b), there have sometimes been earthquakes of M5.0 or over.

For the seismic activity since 1980, in the area around the recent event (Area c), there have sometimes been earthquakes of M6.0 or over.

Japan Meteorological Agency
[Evaluation of Seismic Activities for May 2012 (June 11, 2012)]