October 22, 2016
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On October 21 at 14:07 (JST), there was a Magnitude (M) 6.6 (provisional value) earthquake at a depth of approximately 10 km in the central Tottori prefecture. Maximum seismic intensity 6 Lower was observed in Tottori prefecture with some damage. The maximum earthquake as of October 22 at 17 o’clock is a M5.6 (provisional value) that occurred on the same day at 14:53 with maximum seismic intensity 4. Although slightly decaying, the seismic activity around the M6.6 event is still high, and earthquakes are distributed in the region extending about 10 km in an NNW-SSE direction. After October 21 at 12:00, a slightly concentrated seismic activity was observed in close vicinity of the event.
* The focal mechanism showed a strike-slip fault type with a compression axis in a WNW-ESE direction. This event occurred within a shallow crust. The seismic fault estimated from the focal mechanism and the seismic activity distribution is the left-lateral strike-slip fault extending in an NNW-SSE direction.
* According to the GNSS data, the crustal deformation associated with the recent event is observed: at Hawai observatory (Tottori prefecture), as about 7 cm (provisional value) north-north-eastward movement.
* The seismic activity is similar to that of "the 2000 Western Tottori Prefecture Earthquake" (M7.3), and not so active as that of "the 2016 Kumamoto Earthquake" (M7.3).
* Around Tottori prefecture, there are several examples of consecutive occurrences of similar ones, and also some examples of similar or larger ones after a few months, after the occurrence of a large magnitude earthquake.
* In the region of strong shaking, one should pay attention to an earthquake with the maximum seismic intensity 6 Lower or so, for a week after the occurrence of the earthquake. Especially in a few days after the occurrence of the earthquake, a large magnitude earthquake often occurs.
* The Earthquake Research Committee evaluated that in the northern Chugoku region including the recent seismic activity area, the seismic activity is comparatively active despite of the small number of active faults, and the possibility of occurrence of M6.8 or over earthquake within 30 years as 40 %.