Comprehensive Modeling of Postseismic Slip and Viscoelastic Flow After the 2004 and 2012 Indian Ocean Earthquakes

The 2004 Mw 9.2 Sumatra-Andaman great earthquake has been studied extensively. Most studies have inferred a combination of afterslip and viscoelastic mechanisms to be responsible for the postseismic deformation. Further off the coast of the Andaman islands, the northern terminus of the Ninety-East ridge has historically been a hotspot for seismic activity. On April 11, 2012, the largest intraplate strike-slip earthquakes recorded, Mw = 8.6 and Mw = 8.2, occurred separated by two hours and around 100 km. Previous studies have shown that these events are difficult to constrain geodetically due to the region's complexities and lack of data density, but there are hints that they excited transient slip rate changes on the Andaman portion of the megathrust more than 1000 km away. Despite the attention these large events have deservedly received, there are additional constraints that can be brought to bear in more rigorous dynamical modeling than has been done thus far. In this presentation we use models developed by Sylvain Barbot (RELAX), E.A. Hetland and more basic finite element methods to examine the slip and viscous flow dynamics excited by these large events. We will process data from both the Andaman-Nicobar postseismic GPS array and Sumatran GPS array (SuGAr) to provide additional constraint on postseismic deformation processes, and examine the consistency of inferred slip processes excited by the 2004 and 2012 events. We will use CHAMP magnetic data to infer geometry and depths to the base of the seismogenic zone, assuming that it is found immediately above the high-susceptibility serpentinite body as in Cascadia. Gravity data from both GRACE and CHAMP also will be used to characterize coseismic slip and postseismic viscoelastic flow along the Sunda-Andaman arc.