After the occurrence of the 2010 Mw 7.8 Mentawai tsunami earthquake on the Sunda megathrust in Indonesia, a following 2012 Mw 6.2 earthquake occurred right on the east of the 2010 event with a deeper focal depth. Although the damages caused by this 2012 event were not significant, it is important for us to understand the seismic hazard of the Mentawai seismic gap and its relationship with the 2010 Mw 7.8 earthquake. In this study, we use GPS observations collected before and after the two earthquakes from 17 SuGAr stations to compute coseismic displacement fields of the 2010 Mw 7.8 and the 2012 Mw 6.2 earthquakes. The GPS data are processed using the GAMIT/GLOBK 10.7 software. The time series of the 2007-2010 and 2010-2012 GPS data shows an exponential pattern which means that there were no interseismic phases before the 2010 and 2012 earthquakes. The coseismic displacement fields have been derived based on the GPS time series. The two earthquakes show similar displacement patterns, and the biggest displacements are found at BSAT, SMGY and SLBU stations. The maximum and minimum displacements occur at BSAT and MLKN stations, respectively. The coseismic source modeling has been conducted and shows that the two earthquakes are highly correlated and have filled the Mentawai seismic gap.

Keywords: continuous GPS, crustal deformation, earthquake, Sunda megathrust