[S-SS31_30PO1] 内陸地震への包括的アプローチ

[SSS31-P05] 2011年東北沖地震後の東北日本弧の粘弾性変形過程のモデル化

*芝崎 文一郎¹、中井 仁彦¹、武藤 潤²、飯沼 卓史³ (1.建築研究所国際地震工学センター、2.東北大学大学院理学研究科地学専攻、3.東北大学災害科学国際研究所)

キーワード：2011年東北沖地震, 東北日本弧, 粘弾性変形

The rheological structure of the Northeastern Japan arc crust and the upper mantle is heterogeneous along and transverse to the arc. Shibazaki et al. (2014) developed a model of the stress state of the Northeastern Japan island-arc crust using a finite element method with viscoelasticity and elastoplasticity. They reproduced several elongated low-stress regions transverse to the arc with viscous deformation that corresponds to hot fingers (high-temperature regions in the mantle wedge). The viscous relaxation process after the 2011 Tohoku-oki earthquake could be affected by the existence of low-viscosity regions caused by hot fingers. A three-dimensional (3D) finite element model was developed to investigate the viscoelastic deformation processes with heterogeneous viscosity distribution after the 2011 Tohoku-oki earthquake. The model considers the realistic crustal and mantle structures, viscoelasticity (Maxwell or Burgurs rheology), and coseismic fault slip distribution obtained by Iinuma et al. (2012). For simplicity, only the elastic crust and viscoelastic mantle structure were considered. The westward movement near the trench and eastward movement in the inland region due to viscoelastic relaxation were reproduced, which are consistent with the observations. We also consider the local low viscosity region in the Northeastern Japan arc crust. In this case, extensional viscous strain concentrates on this region. We report the numerical results that take into account the realistic 3D heterogeneous viscosity distribution in the crust and the upper mantle beneath the Northeastern Japan island arc.