Seismic Activity offshore Sanriku beginning on February 17 (1)

(1) Summary
On February 17, 2015 at 08:06 (JST), there was a M6.9 earthquake (maximum seismic intensity 4) offshore Sanriku. The focal mechanism (CMT solution) showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and continental plates. This event occurred within the aftershock area of "the 2011 off the Pacific Coast of Tohoku Earthquake" (hereafter referred to as the Tohoku-Oki Earthquake), which occurred on March 11, 2011.
Japanese Meteorological Agency announced "Tsunami Advisory" for the coast of Iwate prefecture on the same day at 08:09 (canceled at 10:20). In addition to tsunami with height of 27 cm at Kuji Port, Iwate prefecture, slight tsunami was observed along the Pacific coast from Hokkaido to Iwate prefecture.
Afterwards in the vicinity of this event, there was an active seismicity, such as a M6.5 earthquake (maximum seismic intensity 3) on 20th at 13:25. There were 12^* earthquakes with maximum seismic intensity 1 or over until February 28.
*including the M6.9 earthquake occurring on February 17 at 08:06.

(2) Seismic activity
a. Recent seismic activity
For the seismic activity since October 1997, in the vicinity of the recent event (Area a), there have sometimes been earthquakes of M5.0 or over before the occurrence of the Tohoku-Oki Earthquake.
Seismicity has increased after the Tohoku-Oki Earthquake, and there were 10 earthquakes (including 3 of this month) of M6.0 or over.

Japan Meteorological Agency
[Evaluation of Seismic Activities for February 2015 (March 10, 2015)]