15:30 〜 16:30
[J05-P-02] Simulation of postseismic deformation caused by the 2011 Tohoku-Oki earthquake
We are developing a 3-D viscoelastic model using the FEM to understand the postseismic deformation that followed the 2011 Tohoku-Oki earthquake. The question of which elements of the viscoelastic media affect the surface deformation is of particular importance. We first examined the individual effects of two different viscoelastic media, the mantle wedge and the oceanic mantle, which produce almost opposite deformation patterns. The mantle wedge controls eastward motion, uplift of the Pacific coast and offshore regions, and extension across a broad area. In contrast, the oceanic mantle controls dominantly offshore westward motion, subsidence across a broad area, minor uplift of the surrounding areas, and contraction offshore. We then developed four different models to clarify which elements of the viscoelastic media affect the observed surface deformation. The simplest model, with uniform viscosity for all viscoelastic media, could explain the horizontal deformation but not the vertical deformation. The second model, with different viscosities for the mantle wedge and the oceanic mantle, could explain the onshore observations but not those on the seafloor. The third model, which includes a thin weak layer beneath the slab, could essentially explain the near-field onshore and seafloor observations but could not explain the far-field data. The final depth-dependent model was able to explain the far-field data as well as the near-field data. In these typical models, it is of particular importance to consider the different viscosities between the mantle wedge and the oceanic mantle, and to include a thin weak layer beneath the slab. Far-field data as well as near-field data are also important for constraining the viscoelastic structure. Clearly, viscoelastic relaxation alone cannot explain the observed deformation. We are now developing a combined viscoelastic and afterslip model.