December 9, 2014
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On November 22 at 22:08 (JST), there was a Magnitude (M) 6.7 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 aftershock activity has been decreasing. The maximum aftershock as of December 9 at 16 o'clock is a M4.5 event 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. In addition, from November 18 to 19, a slightly concentrated seismic activity (foreshocks) was observed in the vicinity of the recent event.
* The focal mechanism had a compression axis in a WNW-ESE direction. This 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 about 29 cm south-eastward horizontal movement, and about 13 cm vertical subsidence at Hakuba observatory (Nagano prefecture). Also, according to the results of analysis of synthetic aperture radar images observed by the Advanced Land Observing Satellite-2 "DAICHI-2", an areal crustal deformation centered at Hakuba Village, about 30 km length in E-W and N-S directions is found. Large deformation can be seen especially along the Kamishiro fault, west of the main shock epicenter.
Judging from these crustal deformations, the length of the earthquake fault
which slipped is estimated to be about 20 km.
* Result of the field survey shows a ground surface fault in an about 9 km length interval from Hokujo, Hakaba Village to Kamishiro, Hakuba Village. In the vicinity of Hokujo-Shiojima, Hakuba Village, west of the main shock epicenter, was observed the eastside-uplifting ground variation with maximum about 90 cm vertical displacement.
* In the vicinity of this event, there is the Kamishiro fault which is a part of the Itoigawa-Shizuoka tectonic line active fault system. It is considered that this event was caused by the action of a part of the Kamishiro fault and its northward extension.