Earthquake in Central Nagano Prefecture on July 2

On July 2, 2011 at 07:28 (JST), there was a M3.9 earthquake (maximum seismic intensity 3) at a very shallow depth in central Nagano prefecture. The focal mechanism showed a strike-slip fault with a compression axis in a NW-SE direction.
This event is an aftershock of the M5.4 earthquake (maximum seismic intensity 5 Upper) that occurred at 08:16 on June 30. Since the recent event, in the area around the event (Area a), the state of many micro earthquakes has been continuing, as compared with it before the main shock of June 30.

For the seismic activity in and after the Heian period, in the area around the recent event (Area c), there were earthquakes of M6.0 or over in 841, 1725 and 1791. Among them, the earthquake of 1791 (Kansei 3) caused damage with collapsed moats of Matsumoto Castle and many fallen human-habitations and storehouses (Rika-Nenpyo).

Japan Meteorological Agency
[Seismic Activity for July 2011 (August 5, 2011)]