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

We infer the slip distribution and average rupture velocity of the magnitude M-W 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. Slip distribution and rupture velocity are determined simultaneously by means of a non linear inversion method. We find high slip values (similar to 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. We conclude this earthquake did not rupture the whole area of the 1833 event, indicating some slip has still to occur. 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 low damaging observed tsunami.