Ultra-far-field postseismic deformation by rheological structures in mantle wedge: Insight from 2D numerical model with various constitutive relation laws

Megathrust earthquakes generate coseismic and postseismic deformation in the wide area and active seismicity. The postseismic viscoelastic relaxation provides information of mantle and lithosphere rheology. The dislocation creep by this relaxation induced the dynamic stress change on the other fault. Although the far-field postseismic deformation is mainly demonstrated by viscoelastic relaxation, the previous studies on the far-field region have been poorly understood. In this study, we simulate the megathrust earthquake in 2D numerical simulation to quantitatively analyze the impact of viscoelastic relaxation at the far-field. We calculated relaxation times for regression analysis from near to far-field postseismic displacement with homogeneous viscoelastic mantle. We calculate the far-field (i.e., back-arc basin or continent) postseismic displacement applying various viscoelastic structures beneath the near-field region (i.e., mantle wedge). Our results indicate that near-field viscoelastic relaxation of the mantle affects far-field crust. We suggest that near-field viscoelastic relaxation should be sufficiently considered to estimate the structure beneath the far-field.