Sangihe-Talaud 7.2 Mw Earthquake, February 12, 2009

A moment magnitude 7.2 Mw was happen in Kepulauan Talaud, Indonesia on February 12, 2009, local time 01.34, resulting 2 fatalities, 10 heavy injured while other 42 people wounded and over 700 building collapse. More than 5000 citizen were evacuated to avoid the affect of continuous aftershock in magnitude 4 Mw to 6 Mw that are still happening in the region.

This earthquake likely occurred as a result of reverse faulting on or near the plate-boundary system separating the Philippine Sea and Celebes Sea basins. Northeastern Indonesia is characterized by complex tectonics in which motions of numerous small plates are accommodating large-scale convergence between the Philippine Sea and Sunda plates. In the region of today's earthquake, the Philippine Sea plate moves west-northwest with respect to the Sunda plate at a velocity of about 62 mm/year. Locally, arc-arc collision is occurring between the Sangihe and Halmahera micro plates, wedging between them the Molucca Sea micro plate, which subducts beneath both (i.e. to the east and west) and forms an inverted-U-shaped seismic zone. Seismicity within the Molucca Sea plate is active to depths of approximately 260 km to the east and 400 km to the west. The tectonic setting of this region is unique in that it is the only global example of an active arc-arc collision consuming an oceanic basin via subduction in two directions and it drive the area to become one of the most tectonic-active in the world today.

The earthquake occurred approximately 30 km off the western coast of the Pulau Salebabu (Indonesia) in an area that has seen large earthquakes in the past. Since 1986, there have been two earthquakes with magnitude greater than 7 in this region.

USGS data showed that the epicenter located in 3.902 deg N, 126.400 deg E with depth 20 km with magnitude 7.2 Mw. Global CMT Moment Tensor Solution shows that this earthquake caused by thrust faulting with direction of 181 deg NE and dip 37 deg. This earthquake supposed to be potentially trigger tsunami, but it was reported that no tsunami occurred.

The earthquake summary poster from USGS