Joint inversion of afterslip and viscoelastic relaxation following the 2012 Mw 8.6 Indian Ocean earthquake

The April 2012 Mw 8.6 Indian Ocean earthquake is the largest strike-slip earthquake instrumentally recorded. The event ruptured multiple faults and reached great depths down to 60 km, which may have induced significant viscoelastic flow in the asthenosphere. Previous studies (e.g., Sun et al, 2014) have shown that viscoelastic flow is prevalent following such large events. Postseismic studies including both afterslip on the coseismic fault and viscoelastic flow in the upper mantle often involve time-consuming iterative forward modeling. Here, we perform linear inversions for postseismic deformation including both afterslip on the coseismic fault and strain in ductile shear zones, making use of three-dimensional analytical Green's functions for distributed strain in finite volumes. By performing sequences of static inversions over multiple time epochs, we estimate the strain rate and aseismic slip rate evolution following the event. Using empirical relationships for rate-strengthening afterslip and the rheology of olivine, we estimate the afterslip parameter (a-b) and the activation volume of olivine in the dislocation creep regime. In addition, we estimate the basal temperature and find that it is slightly higher than the other regions' for a 60 Myr old oceanic lithosphere.