Viscoelastic relaxation of the upper mantle and afterslip following the 2014 MW 8.1 Iquique earthquake

An improved understanding of postseismic crustal deformation following large subduction earthquakes may help to better understand the rheological properties of upper mantle and the slip behavior of subduction interface.Here we construct a three-dimensional viscoelastic finite element model to study the postseismic deformation of the 2014 M8.1 Iquique, Chile earthquake. Elastic units in the model include the subducting slab, continental and oceanic lithospheres. Rheological units include the mantle wedge, the oceanic asthenosphere and upper mantle.We use a 2 km thick weak shear zone attached to the subduction fault to simulate the time-dependent stressdriven afterslip. The viscoelastic relaxation in the rheological units is represented by the Burgers rheology. We carry out grid-searches on the shear zone viscosity, thickness and viscosity of the asthenosphere, and they are determined to be 10Pa s, 110 km and 2 × 10Pa s, respectively. The stress-driven afterlsip within the first two years is up to ～47 cm and becomes negligible after two years(no more than 5 cm/yr). Our results suggest that a thin, low-viscosity oceanic asthenosphere together with a weak shear zone attached to the fault are required to better reproduce the observed postseismic deformation.