Coseismic deformation of the 2007 Sumatra earthquakes from InSAR

On the 12 September 2007 magnitude 8.5 and 7.9 earthquakes occurred in Southern Sumatra as the result of thrust faulting on the subduction zone of the Indo Australian plate under the Sunda plate. The magnitude 8.5 earthquake, located 130 km SW of Bengkulu, Sumatra, is the fourth earthquake of magnitude greater than 7.9 on this plate boundary during the past decade. The magnitude 7.9 earthquake occurred about 12 hour later and about 225 km northwest of the magnitude 8.5 earthquake. We examine the deformation caused by these earthquakes on the Sumatra islands using InSAR data. The SAR interferogram obtained from ALOS-PALSAR data acquired on January 29, 2007 and September 16, 2007 shows a significant crustal deformation in Bengkulu although the epicenter is located more than 100 kilometers westward. The deformation reaches more than 60 cm toward the satellite located 75 kilometers northwestward from Bengkulu. Westward, the Pagai islands deformation (South Pagai Island: Pulau Pagai Selatan and North Pagai Island Pulau Pagai Utara) is studied with an interferogram obtained from data of the June 21, 2007 and September 21, 2007. These islands are closer to the earthquake source fault so the maximum crustal deformation is more significant and reaches approximately 1.8m. This deformation occurs between the south end of the South Pagai Island and the north end of the North Pagai Island, meaning that the South island has moved 1.8m toward the satellite relative to the North Island.