Source process of the September 12, 2007 MW 8.4 Southern Sumatra earthquake from tsunami tide gauge record inversion

Abstract

We infer the slip distribution and average rupture velocity of the magnitude MW 8.4 September 12, 2007, Southern Sumatra earthquake from available tide-gauge records of the ensuing tsunami. We select 9 waveforms recorded along the west coast of Sumatra and in the Indian Ocean. We assume the fault plane and the slip direction to be consistent with both the geometry of the subducting plate and the early focal mechanism solutions. Slip distribution and rupture velocity are determined simultaneously by means of a non linear inversion method. We find high slip values (∼10 m) into a patch 100 km long and 50 km large, between 20 and 30 km of depth, about 100 km north-west from the epicenter. Our estimate of rupture velocity is of 2.1±0.4 km/sec. The relatively large depth of the main slip patch is the likely explanation for the small observed tsunami.