Earthquake in Northern Tochigi Prefecture on February 25

On February 25, 2013 at 16:23 (JST), there was a M6.3 earthquake (maximum seismic intensity 5 Upper) at a depth of 3 km in northern Tochigi prefecture. This event occurred within the crust The focal mechanism showed a strike-slip fault with a compression axis in a WNW-ESE direction. In the vicinity of this event (Area a), seismicity was seen after about February 23, and there was a M3.6 earthquake (maximum seismic intensity 3) at 15:26, about one hour before, on February 25. Brisk aftershock activity was seen after this event, and there was a M4.7 earthquake (maximum seismic intensity 4) at 16:34 on the same day. There were 60 aftershocks with a maximum seismic intensity 1 or over by March 6.
For the seismic activity since October 1997, in the vicinity of the recent event (Area a), there have been few earthquakes of M2.0 or over. After "the 2011 off the Pacific Coast of Tohoku Earthquake", seismicity increased and there was a M3.7 earthquakes (maximum seismic intensity 3) on December 17, 2012.

For the seismic activity since January 1923, in the region around the recent event (Area b), there was the Imaichi Earthquake (M6.4) on December 26, 1949, and it caused damage with 10 fatalities, 163 injured persons, 290 totally destroyed houses (Comprehensive Bibliography of Destructive Earthquakes in Japan, Latest Edition). Except for the Imaichi Earthquake and its aftershocks, in the region around the recent event, there was almost no earthquake of M5.0 or over.

Japan Meteorological Agency
[Evaluation of Seismic Activities for February 2013 (March 11, 2013)]