November 23, 2014
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On November 22 at 22:08 (JST), there was a Magnitude (M) 6.7 (provisional value) earthquake at a depth of approximately 5 km in the northern Nagano prefecture. Maximum seismic intensity 6 Lower was observed in Nagano prefecture with some damage. Afterwards the seismic activity shows a type of main shock - aftershock sequence. The maximum as of November 23 at 15 o'clock is a M4.5 (provisional value) aftershock that occurred on the same day at 22:37 with maximum seismic intensity 5 Lower. Aftershocks are distributed about 20 km in an N-S direction, from Otari Village to Hakuba Village along the Hime river. From November 18 to 19, a slightly concentrated seismic activity was observed in the vicinity of the event.
* The focal mechanism had a compression axis in a WNW-ESE direction. The event occurred at shallow depth in the crust. The seismic fault estimated from the aftershock distribution and the focal mechanism of the main shock is the eastward-dipping reverse fault extending in an N-S direction.
* According to the GNSS data, the crustal deformation associated with the main shock is observed: at Hakuba observatory (Nagano prefecture), about 29 cm south-eastward horizontal movement, and about 12 cm vertical subsidence (provisional).
* In the vicinity of this event, there is the Kamishiro fault which is a part of the Itoigawa-Shizuoka tectonic line active fault system. Although the possibility is high that this event was caused by the action of a part of the Kamishiro fault, we need more research and observation results to derive the details of the mechanism.