3D numerical model for viscoelastic postseismic deformation following the Maule M_W8.8 earthquake in 2010

The 2010 M_W8.8 Maule earthquake occurred near the plate boundary between the Nazca plate and the South American plate. The earthquake produced significant coseismic and postseismic deformation. The maximum coseismic motion is about 5 m in the horizontal direction and about 5 cm subsidence. After correcting the GPS data for secular, seasonal and annual trends, the postseismic cumulative motion within the first 6 years after the earthquake include up to about 68 cm in the horizontal direction and up to 20 cm uplift. The three-dimensional （3D） viscoelastic structure can be constrained by the postseismic deformation of the 2010 earthquake. We have constructed a 3D finite element model to study the effects of the rheological structure on the postseismic deformation of the 2010 earthquake. We assume the viscoelasticrelaxation of the upper mantle to be represented by the Burgers rheology. And in the paper, a 2 km thick weak shear zone attached to the megathrust is used to simulate the afterslip. Based on the comparison with the GPS observation data, the preferred model determined that a 120 km thick asthenosphere with a viscosity of 1×10¹⁹ Pa·s at the top of the oceanic upper mantle is required to fit the data. The afterslip simulated by shear zone with a viscosity of 5×10⁷ Pa·s is up to 2 m in the first 2 years and decays rapidly with time.