Coseismic and postseismic deformation of the great 2004 Sumatra-Andaman Earthquake
The 26 December 2004 M9.2 Sumatra-Andaman earthquake (SAE) induced a devastating tsunami when it ruptured over 1300 km of the boundary between the Indo-Australian plate and Burma microplate (Vigny et al., 2005; Bilek, 2007). Three months later on 28 March 2005, the M8.7 Nias earthquake (NE) ruptured over 400 km along the same trench overlapping and progressing to the south of the M9.2 rupture (Banerjee et al., 2007). The spatial and temporal proximity of these two earthquakes suggests that the SAE mechanically influenced the timing of the NE. I analyze the coseismic and postseismic deformation, stress, and pore pressure of the 2004 SAE using 3D finite element models (FEMs) in order to determine the mechanical coupling of the SAE and NE. The motivation for using FEMs is two-fold. First, FEMs allow me to honor the geologic structure of the Sumatra-Andaman subduction zone, and second, FEMs simulate the mechanical behavior of quasi-static coseismic and postseismic deformation systems (e.g., elastic, poroelastic, and viscoelastic materials). The results of my study include: 1) Coseismic slip distributions are incredibly sensitive to the distribution of material properties (Masterlark and Hughes, 2008), 2) Slip models derived from tsunami wave heights do not match slip models derived from GPS data (Hughes and Masterlark, 2008), 3) These FEMs predict postseismic poroelastic deformation and viscoelastic deformation simultaneously (Masterlark and Hughes, 2008), 4) Pore pressure changes induced by the SAE triggered the NE via fluid flow in the subducting oceanic crust and caused the NE to occur 7 years ahead of interseismic strain accumulation predictions (Hughes et al., 2010; Hughes et al., 2011), 5) Global Conductance Matrices provide a way to smooth an underdetermined FEM for arbitrarily irregular surfaces, and 6) FEMs are capable and desired to model subduction zone deformation built around the complexity of a subducting slab which is usually ignored in geodetic studies (Masterlark and Hughes, 2008; Hughes et al., 2010). Rapidly advancing computational capabilities recently placed FEMs at the forefront of earthquake deformation analyses. The results and conclusions of this study will strongly influence future analyses of coseismic and postseismic deformation, stress, pore pressure, and tsunami genesis.