Western Tottori, Japan, Earthquake (Mw6.6) Main Aftershocks
Observations History
Research Center for Earthquake Prediction, DPRI, Kyoto University Links *JAPANESE*

- Seismometers -
- GPS -
- Electro-magnetic -


On the afternoon of October 6 at 13:30 JST (0430 GMT) a significant earthquake (Mw 6.6 Freesia, Mw 6.6 Harvard, M7.3 JMA) occurred in western Tottori prefecture in western Japan. The closest large city is Matsue in Shimane prefecture, 30 km northwest of the earthquake. There were more than 100 people injured but no fatalities reported to date.

Focal mechanisms show that the mainshock was a strike-slip fault with nodal planes striking northeast and northwest (243 and 153 from Earthquake Research Institute, Univ. of Tokyo, 241 and 152 from the Freesia network, Science and Technology Agency, 330 and 240 from Harvard ). The aftershock distribution is elongated in the northwest-southeast direction, indicating left-lateral faulting on a northwest-southeast striking fault.

The shaking intensity, as measured by the JMA scale,  had maximum values of 6+ in the vicinity of the epicenter.  The event was felt over a large region of western Japan with intensity 4 in Kyoto and Kobe, and intensity 3 in Osaka."
The epicenters of aftershocks located by the Disaster Prevention Research Institute, Kyoto University roughly show a line that extents for about 25 to 30 km.

There are no reports of large surface rupture , cracks and surface deformation have been reported at several sites close to the aftershock trend.

There are no large mapped faults in the region that have the same trend as the aftershocks.

There have been 7 magnitude 4 to 5 earthquakes in this region since 1989 that also occurred on a northwest-southeast trend very close to the aftershocks of the October 6 event.

The Working Group for Compilation of 1:2,000,000 Active Faults Map of Japan, New 1:2,000,000 Active Faults Map of Japan (in Japanese), Active Fault Research, 19, 3-12, 2000