September 10, 2009
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On August 11, at 05:07 (JST) there was a M6.5 earthquake at a depth of approximately 25km under Suruga Bay. This event had a maximum seismic intensity 6 Lower in Shizuoka prefecture, and caused some damage. Tsunamis were observed along the Pacific coast in the area between Suruga Bay and the Tokai region, with a tsunami height of 0.4m in Omaezaki city. (see the 200th Evaluation of the Earthquake Research Committee " Seismic Activity under the Suruga Bay on August 11, 2009")
* Seismic activity is a main shock - aftershock sequence. It has gradually been declining. Aftershocks were distributed along approximately 20km in a NW-SE direction, with the main shock located in the southeast area. In addition, the aftershocks were distributed dipping to the northeast in the northwestern area, and dipping to the south in the southeastern area. The largest aftershock was a M4.5 event at 18:11 on August 13.
* The focal mechanism of the main shock showed a reverse fault with a strike-slip component and a compression axis in a NNE-SSW direction. Judging from the source depth, the focal mechanism, and the aftershock distribution, this event occurred within the Philippine Sea plate.
* According to the GPS data and the leveling results, small crustal movements associated with this event were observed in the vicinity of Suruga Bay, with a displacement of approximately 1cm to the west at the Yaizu-A station (Shizuoka prefecture). The crustal movements in the GPS data show that the source faults are reverse faults with strike-slip components for both the northwest and southeast areas, which corresponds to the focal mechanism and the aftershock distribution.
* This event occurred close to the expected focal region of the so-called Tokai Earthquake. However, it occurred within the Philippine Sea plate, which is a different mechanism from that of the expected so-called Tokai Earthquake. The Japan Meteorological Agency announced that there was no crustal movement that might be directly associated with the so-called Tokai Earthquake.
(Underlined parts are amendments or additions to the 200th Evaluation of the Earthquake Research Committee.)