Influences of the heterogeneity of viscoelastic medium on postseismic deformation of the 2008 MW7.9 Wenchuan earthquake

Abstract

The study of postseismic deformation is important for constraining the viscoelastic properties of the Earth and inverting the post-earthquake process. The levelling survey revealed that the area near Beichuan elevated 5.3 cm about two years after the MW7.9 Wenchuan earthquake (05/12/2008), during which the area underwent significant downward movement. The GPS horizontal displacements showed a non-monotonic variation after the Wenchuan earthquake. In this study, a 3-D viscoelastic finite element model is employed to simulate the coseismic and postseismic deformation of the Wenchuan earthquake. The numerical simulations show that the lateral heterogeneity across the Longmenshan fault plays an important role in the postseismic displacements. The results reveal that the coseismic deformation is not sensitive to the horizontal heterogeneity, but the postseismic deformation is sensitive to it. The postseismic deformation of the horizontally heterogeneous model is generally consistent with the observations of all geodetic surveys, such as GPS, InSAR and levelling, but not for the horizontally homogenous model. We also find that the non-monotonous variation of the postseismic deformation of the Wenchuan earthquake could be explained by a viscoelastic relaxation model with lateral heterogeneous medium across the Longmenshan fault.