We investigated the source process of the 2010 Mentawai earthquake by joint inversion method using near source and teleseismic body-wave data. To perform a stable inversion, we applied smoothing constraints and determined their relative weights on the observed data using ABIC criterion. The teleseismic waveforms were windowed for 150 sec, band-passed between 0.001 and 1.0 Hz, and then integrated into displacement. The strong motion data were windowed for 250 sec, band-passed between 0.005 and 0.5 Hz, and then integrated into velocity. The re-sampling rate for both data set to be 0.25 sec. We estimated the fault area to be 190 × 70 km2. The main source parameters are as follows: (strike, dip, rake) = (324⁰, 10⁰, 94.6⁰); the depth of hypocenter 13.5 km; the seismic moment 5.814×1020 Nm (Mw 7.8); source duration 102 sec; and the maximum slip amounts to 3.9 m.
The source rupture process obtained probably can be divided into 2 stages. At stage 1, the rupture nucleated near the hypocenter and then propagated to the southwestward and broke the first asperity centering at 14 km from the epicenter. At stage 2, the rupture propagated to the northwestward and broke the second asperity which was centered about 78 km from the epicenter. Our total slip distribution is well consistent with the result of tsunami waveform analysis by Satake et al. (2011). This earthquake was categorized as a tsunami earthquake due to the long rupture duration and the generation of tsunami much larger than expected for its magnitude.