Earthquake Offshore Miyagi Prefecture on May 13

On May 13, 2015 at 06:12 (JST), there was a M6.8 earthquake (maximum seismic intensity 5 Upper) at a depth of 46 km, offshore Miyagi prefecture. The focal mechanism (CMT solution) showed a reverse fault type with a compression axis in an E-W direction. This event occurred at the boundary between the Pacific and the continental plates.
For the seismic activity since October 1997, in the vicinity of the recent event (Area b), before "the 2011 off the Pacific coast of Tohoku Earthquake," there have been earthquakes of M3 to M4 several times per year, except for a M6.3 earthquake (maximum seismic intensity 5 Lower) occurring on November 3, 2002. After the 2011 Tohoku Earthquake, the seismicity increased than before. On July 23, 2011, there was a M6.4 earthquake (maximum seismic intensity 5 Upper), which caused damage with 2 partially collapsed houses and so on (Fire and Disaster Management Agency). After the 2011 Tohoku Earthquake, there have been 5 earthquakes of M6.0 or over including the recent event, the last being the largest.
For the seismic activity since January 1923, in the region around the recent event (Area c), there have sometimes been earthquakes of M7.0 or over, such as "the 1978 Miyagiken-Oki Earthquake" (M7.4) occurring on June 12, 1978.

Japan Meteorological Agency
[Evaluation of Seismic Activities for April 2015 (May 14, 2015)]