Insight into present-day deformation of the Sundaland plate from GPS CORS measurements

Over the past decade, the Sunda megathrust and neighbouring region has shown a high potential for generating great earthquakes. Three thrust-fault (2004 Mw9.1 Aceh, 2005 Mw8.6 Nias and 2007 Mw8.5 Bengkulu) and two strike-slip (2012 Mw8.6 and 8.2 northern Sumatra) earthquakes of ≥M8 have created widespread deformation of the Sundaland plate. The observed geodetic strain rate, induced by the series of great earthquakes, is associated with the postseismic viscoelastic rebound and afterslip on the western margin of Sundaland plate. This study is based on sixteen years (1999-2014) of GPS Continuously Operating Reference Station (CORS) data from over 100 sites that span the Sundaland plate. The transient effect of postseismic deformation has caused a complex pattern of GPS secular velocities extending from the Sunda trench to the central region of Peninsular Malaysia. The average velocity of GPS CORS with respect to ITRF2008 in Peninsular Malaysia from before Aceh-Nias earthquakes, between Nias-northern Sumatra earthquakes, and post-northern Sumatra earthquake; are 31.2±2.0 mm/yr S81°E, 20.8±5.6 mm/yr S61°E, and 25.0±2.3 mm/yr S76°E, respectively with 1σ uncertainties. The vector variation shows that the postseismic transients deformation has a significant effect on the regional velocity field. This study examines the strain rates associated with transient postseismic relaxation of these earthquakes. The interseismic shear strain rates of Sundaland plate is useful for indicating the creeping and locked segments of the Sunda forearc, from the Simeulue to Enggano Island, thus improving our understanding of tectonics deformation in Sundaland megathrust.