Earthquake Offshore Fukushima Prefecture on March 16 (2) Seismic Activity (1)

a. details of earthquake generating place and aftershock activity
On March 16, 2022 at 23:34 (JST), there was an M6.1 earthquake (maximum seismic intensity 5 Lower) at a depth of 57 km, offshore Fukushima prefecture. 2 minutes later, at 23:36 (JST) there was an M7.4 earthquake (maximum seismic intensity 6 Upper) at a depth of 57 km, offshore Fukushima prefecture. Both the focal mechanisms (CMT solution for the M7.4 earthquake) of these earthquakes showed a reverse fault type with a compression axis in a WNW-ESE direction. These events occurred within the Pacific plate. Then in the vicinity of these events, the seismic activity became high and from March 16 till 31 there occurred 5 earthquakes with M5.0 or over, such as an M5.5 earthquake (maximum seismic intensity 4) (within the Pacific plate) on 17^th at 00:52 (JST), an M5.0 (maximum seismic intensity 3) (within the Pacific plate) on 19^th at 00:57 (JST), and an M5.2 (maximum seismic intensity 4) (at the boundary between the Pacific and the continental plates) on 25^th at 12:08 (JST).
For the seismic activity since October 1997, in the vicinity of the recent event (Area b), the seismic activity was stationary and there have often been earthquakes of M4.0 or over, even before the occurrence of "the 2011 off the Pacific coast of Tohoku Earthquake" (hereinafter referred to as the Tohoku-Oki Earthquake). After the Tohoku-Oki Earthquake, the seismic activity became higher and the state of many earthquake generation continues: including the recent event, there have been 8 earthquakes of M6.0 or over. On February 13, 2021, there was an M7.3 earthquake (maximum seismic intensity 6 Upper) at almost the same place as the recent event.

Japan Meteorological Agency
[Evaluation of Earthquake Offshore Fukushima Prefecture on March 16, 2022 (April 11, 2022)]