[S-CG46] スラブ内地震とその発生メカニズム

[SCG46-05] Numerical modeling of subduction and evaluation of the Philippine Sea plate tectonic history along the Nankai Trough

*Erika Moreno¹、Vlad Constantin Manea²、Marina Manea²、Nobuaki Suenaga¹、Shoichi Yoshioka^1,3 (1.Research Center for Urban Safety and Security, Kobe University, Kobe 657-8501, Japan.、2.Computational Geodynamics Laboratory, Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76230, México.、3.Department of Planetology, Kobe University, Kobe 657-8501, Japan.)

キーワード：numerical simulations, Velocity and age parameters, Tectonic evolution, Subduction, Initial dip angle

The subduction of the Philippine Sea plate (PHS) along the Nankai Trough is relatively young compared with subduction along the Japan Trench. Although the current arc volcanism distribution in the Chugoku region is distinctly related to the evolution of subduction angle of the PHS plate in the past 15 Ma, the tectonic evolution of the PHS plate along the Nankai Trough is still controversial and is not fully understood. There are several hypotheses based on different estimates for the convergence rate and plate age along the Nankai Trough. Studies based on the traditional migrating of a triple junction propose a cessation period of the PHS plate subduction between ~12 Ma and ~ 6 Ma, followed by a gradual increasing in the convergence rate until the present with a maximum velocity of ~ 5 cm/yr. Other studies based of the nature and volcanism distribution in the Chugoku region suggest a higher convergence rate between ~15 Ma and ~ 3 Ma, followed by a constant convergence rate of ~ 5.7 cm/yr from 3 Ma to the present. Given the existence of such contrasting tectonic evolution scenarios along the Nankai Trough, we propose a numerical study with high-resolution 2D visco-elasto-plastic numerical models of spontaneous subduction that allow us to better understand how subduction parameters affect the PHS plate subduction dynamics. Our study is focusing on the Chugoku region and we contrast tectonic evolution scenarios against the slab geometry after a 15 Myr time integration. Our modeling strategy involves a parameter study where the initial slab geometry as well as various subduction parameters is analyzed in terms of subduction geometry evolution. Preliminary numerical simulations predict that convergence rate and plate age variations play an important role in the evolution of subduction geometry. The simulation set based on the traditional migrating of a triple junction shows a steep slab angle that is not consistent with the present-day geometry. We also observed that this result is independent of the initial slab dip angles (25º - 30º) employed in this study. On the other hand, the best results are obtained for numerical models obtained for tectonic studies that propose a higher convergence rate between ~15 Ma and ~ 3 Ma. We conclude that our study shows that the predictive nature of numerical simulations of spontaneous subduction can be successfully employed to distinguish between different tectonic evolutionary scenarios along the Nankai Trough.