August 11, 2009
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Seismic Activity under the Suruga Bay on August 11, 2009

* On August 11, at 05:07 (JST) there was a M6.5 (provisional) 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 on the Pacific coast in Shizuoka prefecture, with a tsunami height of 0.4m in Omaezaki city.

* The focal mechanism had a compression axis in a NNE-SSW direction. Judging from the focal mechanism, the aftershock distribution, and the source depth, it is thought that this event occurred within the Philippine Sea plate.

* Seismic activity is a main shock-aftershock sequence. The largest aftershock as of 18:30 on August 11 was a M4.3 (preliminary) event at 18:09 on August 11.

* According to the GPS data, crustal movements associated with the main shock were observed in the vicinity of this event, with a displacement of approximately 2cm to the west at the Yaizu-A station (Shizuoka prefecture).

* 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 associated with the so-called Tokai Earthquake.