Abstract
Great earthquakes (≥M8.0) often cause widespread postseismic decay in areas well beyond any recognised plate boundaries. The M
8.6 and 8.2 northern Sumatra doublet earthquakes occurred on 11 April 2012, near the intersection of the Indian, Australian and Sundaland plate, have caused an extensive coseismic offset and postseismic decay over the region. In this study, the long-term GPS time-series (1999–2014) suggests that the postseismic decay associated with the doublet earthquakes have had a significant effect on the eastern boundary of the Sundaland plate up to the western region of Peninsular Malaysia. Before the 2004 M
9.1 Aceh and 2005 M
8.6 Nias earthquakes, the average velocity of continuous GPS sites in Peninsular Malaysia is moving southeastward at
relative to the fixed Australian plate. The postseismic decay of these two great earthquakes has caused Peninsular Malaysia to experience elastic relaxation rebound into the south-southeast direction with a lower average velocity of
. After 2012 northern Sumatra earthquakes, Peninsular Malaysia returns to its original course of motion before the 2004 and 2005 earthquakes, with slightly lower average velocity at
. In this paper, the impact of coseismic and postseismic deformation of the 2012 M
8.6 and 8.2 northern Sumatra earthquakes towards Sundaland plate vectors are discussed. A new rotation vector for the Sundaland plate is defined in ITRF2008 by using 10 selected cGPS sites that are assumed to be in the stable block, based on the 1999–2004 time-series data.