Earth Planets Space, Vol. 58 (No. 1), pp. 63-67, 2006LETTER
Takumi Matsumoto1, Yoshihiro Ito1, Hirotoshi Matsubayashi1, and Shoji Sekiguchi1
1National Research Institute for Earth Science and Disaster Prevention, Tennodai, 3-1, Tsukuba, Ibaraki 305-0006, Japan
(Received August 10, 2005; Revised November 22, 2005; Accepted November 28, 2005; Online published January 27, 2006)
The 2005 West Off Fukuoka Prefecture Earthquake with a Japan Meteorological Agency (JMA) magnitude (MJMA) of 7.0 occurred on March 20, 2005. We determined moment tensor solutions, using a surface wave with an extended method of the NIED F-net routine processing. The horizontal distance to the station is rounded to the nearest interval of 1 km, and the variance reduction approach is applied to a focal depth from 2 km with an interval of 1 km. We obtain the moment tensors of 101 events with (MJMA) exceeding 3.0 and spatial distribution of these moment tensors. The focal mechanism of aftershocks is mainly of the strike-slip type. The alignment of the epicenters in the rupture zone of the main-shock is oriented between N110°E and N130°E, which is close to the strike of the main-shock's moment tensor solutions (N122°E). These moment tensor solutions of intermediate-sized aftershocks around the focal region represent basic and important information concerning earthquakes in investigating regional tectonic stress fields, source mechanisms and so on.
Key words: The 2005 West Off Fukuoka Prefecture Earthquake, moment tensor, broadband seismometer, seismicity, F-net.