Earthquake Off-shore of Matsumae [Off-shore Southwest of Hokkaido] on July 28

On July 28, 2009 at 20:52 (JST), there was a M4.0 earthquake at a depth of 8km, off-shore of Matsumae [off-shore southwest of Hokkaido] (maximum seismic intensity 4). This event occurred within the crust. The focal mechanism had a compression axis in a NW-SE direction. At nearly the same place, there was a M3.2 earthquake (maximum seismic intensity 2) on July 9 (19 days before the recent event), and a M3.3 earthquake (maximum seismic intensity 2) on August 7 (10 days after the recent event).
In the vicinity of the recent event (Area b), there was a sequence of seismicity with seven earthquakes equal to or larger than M4.0 during the period from October 1995 through 1997. The largest earthquake was the M4.7 event on May 5, 1997 (maximum seismic intensity 3).

For the seismic activity since August 1923, there have been no earthquakes equal to or larger than M5.0 in the region near the recent event (Area c).

[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.

Japan Meteorological Agency
[Seismic Activity for July 2009 (August 10, 2009)]