Tsunami waveform inversion of the 2007 Bengkulu, southern Sumatra, earthquake

Asbtract

We performed tsunami waveform inversions for the Bengkulu, southern Sumatra, earthquake on September 12, 2007 (M_w 8.4 by USGS). The tsunami was recorded at many tide gauge stations around the Indian Ocean and by a DART system in the deep ocean. The observed tsunami records indicate that the amplitudes were less than several tens of centimeters at most stations, around 1 m at Padang, the nearest station to the source, and a few centimeters at the DART station. For the tsunami waveform inversions, we adopted 20-, 15- and 10-subfault models. The tsunami waveforms computed from the estimated slip distributions explain the observed waveforms at most stations, regardless of the subfault model. We found that large slips were consistently estimated at the deeper part (>24 km) of the fault plane, located more than 100 km from the trench axis. The largest slips of 6–9 m were located about 100–200 km northwest of the epicenter. The deep slips may have contributed to the relatively small tsunami for its earthquake size. The total seismic moment is calculated as 4.7 × 10²¹ N m (M_w = 8.4) for the 10-subfault model, our preferred model from a comparison of tsunami waveforms at Cocos and the DART station.