Seismic Activities from Hamadori, Fukushima Prefecture to Northern Ibaraki Prefecture
Within the crust from Hamadori, Fukushima prefecture through northern Ibaraki prefecture (Area b), seismicity increased after the 2011 off the Pacific Coast of Tohoku Earthquake. As of late January 2012, it has been declining as a whole, but it continues. Many of the focal mechanisms in this seismicity showed a normal fault. The direction of their tension axes is regionally different. It is an NW-SE direction on the whole in the northern region, and an ENE-WSW direction on the whole in the southern region.
As of late January 2012, the largest was a M7.0 earthquake (maximum seismic intensity 6 Lower) on April 11, 2011 at a depth of 6 km in Hamadori, Fukushima prefecture. This event caused damage with 4 fatalities and 10 injured persons (Fire and Disaster Management Agency).
During January 2012, on January 5 at 22:13 (JST), there was a M4.2 earthquake (maximum seismic intensity 4, normal fault with a tension axis in an ENE-WSW direction) at a depth of 6 km in Nakadori, Fukushima prefecture, and there were 32 earthquakes of M3.0 or over in Area b. In addition, there were 6 earthquakes with a maximum seismic intensity 3 or over (maximum seismic intensity 4: 1, maximum seismic intensity 3: 5).
Japan Meteorological Agency
[Evaluation of Seismic Activities for January 2012 (February 9, 2012)]