Source model of the 2009 Mw 7.6 Padang intraslab earthquake and its effect on the Sunda megathrust

Abstract

We investigate the source of the Mw 7.6 Padang earthquake by inverting three-component global positioning system (GPS) data and broad-band regional seismic-displacement waveforms. The earthquake involved oblique-reverse slip either on an E–W, south-dipping plane, or on a N–S, west-dipping plane. Finite-fault inversions indicate that the rupture primarily propagated downdip and southwest from the hypocentre, with a scalar seismic moment between 3.4 and 3.7 × 1020 N m (Mw 7.62–7.65). Analysis of the seismic and geodetic data do not allow for unique identification of the causative focal plane. Aftershock patterns strongly suggest the E–W plane was the causative focal plane, but aligned geological structures in the downgoing plate favour the N–S plane. In either case, this unusually large intraslab earthquake has moved closer to failure the deepest portion of the overlying megathrust, which last ruptured during a great earthquake more than two centuries ago and is late in its seismic cycle.