Numerical investigation for the effect of the subducting slab geometry on the postseismic deformation using finite element method

초록

The geodetic techniques enable the observation of time-series surface displacement during an earthquake cycle, which provides accurate coseismic and postseismic information. Many geodynamic studies have tried to explain the postseismic deformation of the mantle beneath the seismic fault based on viscoelastic stress-strain relation. Megathrust earthquakes generating coseismic and postseismic deformation throughout a wide area provide a chance to invert the mantle viscosity beneath the intraplate region and plate boundaries. In this study, we performed a series of finite element numerical simulations of near- and far-field postseismic deformation associated with megathrust earthquakes to investigate the effects of mantle viscosity and subducting slab geometry (i.e., slab angle) on viscoelastic relaxation. We found the seaward postseismic horizontal displacement in most areas in the overriding plate one year after the earthquake. Our model showed that the smaller mantle viscosity and larger slab angle lead to the larger postseismic horizontal displacement. This trend is maintained even in the remote geodetic station located similar to 1000 km far from the megathrust fault. For instance, the horizontal displacement is 11.5 cm when the slab angle =50 degrees and mantle viscosity= 10(18) Pa. s. In contrast, the displacement is extremely small as 0.9 cm with the slab angle =20 degrees and mantle viscosity = 10(19) Pa.s. We demonstrate that the slab angle can influence the postseismic relaxation in distant locations from the fault. Furthermore. we suggest that the postseismic deformation model for estimating the mantle viscosity of remote regions should consider the detailed geometry of the subducting slab.

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