CO-SEISMIC DEFORMATION OF THE 2 SEPTEMBER 2009 SOUTH JAVA EARTHQUAKE FROM GPS OBSERVATIONS

The South Java earthquake with magnitude of 7.0 Mw, occurred on 2 September 2009 at about 02:55 pm local time. The epicenter is located in the sea, about 142 km southwest of Tasikmalaya at the depth of about 38 km, with geographical coordinates of about 8.24S (latitude) and 107.32E (longitude). The shaking of earthquake was felt in most regions of Java Island and even in Bali Island which is about 850 km from the epicenter. The latest report on 3 September 2009 informed that this earthquake has destroyed about 11,000 houses and buildings, killed 46 peoples, injured about 240 peoples and causes landslides at a few locations. Moreover, about 40 peoples are reported still missing and about 3100 peoples have to be evacuated. Along the Java trench the Australian-Oceanic plate is moving and pushing on to and subducting beneath the Java continental crust at a relative motion of about 60 mm/yr in NNE direction at the longitude of the earthquake. This subduction-zone process imposes tectonic stresses on the fore-arc region offshore and on land of Java, thus causes the formation of earthquake fault zones to accommodate the plate movement. At present, there is still question whether the September 2009 South Java earthquake is an intra-slab or intra-plate earthquake. Preliminary processing results from seven continuous GPS stations of BAKOSURTANAL located at Pameungpeuk, Sagaranten, Ujung Genteng, Jampang Kulon, Cisolok, Lido and Cibinong, which are located about 120 to 150 km from the epicenter, show the co-seismic deformation of up to about a few cm level. However, more rigorous processing is now underway to estimate more precisely the co-seismic deformation. GPS campaign at about 40 existing GPS stations along the coastal areas of West Java region will also soon be conducted in order to obtain a more detail characteristics of co-seismic deformation and earthquake mechanism.