Rupture process of the 2010 Mw 7.8 Mentawai tsunami earthquake from joint inversion of near-field hr-GPS and teleseismic body wave recordings constrained by tsunami observations

The 25 October 2010 Mentawai tsunami earthquake (M w 7.8) ruptured the shallow portion of the Sunda megathrust seaward of the Mentawai Islands, offshore of Sumatra, Indonesia, generating a strong tsunami that took 509 lives. The rupture zone was updip of those of the 12 September 2007 M w 8.5 and 7.9 underthrusting earthquakes. High-rate (1 s sampling) GPS instruments of the Sumatra GPS Array network deployed on the Mentawai Islands and Sumatra mainland recorded time-varying and static ground displacements at epicentral distances from 49 to 322 km. Azimuthally distributed tsunami recordings from two deepwater sensors and two tide gauges that have local high-resolution bathymetric information provide additional constraints on the source process. Finite-fault rupture models, obtained by joint inversion of the high-rate (hr)-GPS time series and numerous teleseismic broadband P and S wave seismograms together with iterative forward modeling of the tsunami recordings, indicate rupture propagation~50 km up dip and~100 km northwest along strike from the hypocenter, with a rupture velocity of~1.8 km/s. Subregions with large slip extend from 7 to 10 km depth~80 km northwest from the hypocenter with a maximum slip of 8 m and from~5 km depth to beneath thin horizontal sedimentary layers beyond the prism deformation front for~100 km along strike, with a localized region having >15 m of slip. The seismic moment is 7.2 × 10 20 N m. The rupture model indicates that local heterogeneities in the shallow megathrust can accumulate strain that allows some regions near the toe of accretionary prisms to fail in tsunami earthquakes