Dynamic rupture of the 2011 Mw 9.0 Tohoku‐Oki earthquake: Roles of a possible subducting seamount

[1] Using a hybrid MPI/OpenMP parallel finite element method for spontaneous rupture and seismic wave propagation simulations, we investigate features in rupture propagation, slip distribution, seismic radiation, and seafloor deformation of the 2011 Mw 9.0 Tohoku-Oki earthquake to gain physical insights into the event. With simplified shallow dipping (10°) planar fault geometry, 1D velocity structure, and a slip-weakening friction law, we primarily investigate initial stress and strength conditions that can produce rupture and seismic radiation characteristics of the event revealed by kinematic inversions, and seafloor displacements observed near the epicenter. By a large suite of numerical experiments aided by parallel computing on modern supercomputers, we find that a seamount of a dimension of ∼70 km by 23 km just updip of the hypocenter on the subducting plane, parameterized by higher static friction, lower pore fluid pressure, and higher initial stress than surrounding regions, may play a dominant role in the 2011 event. Its high strength stalls updip rupture for tens of seconds, and its high stress drop generates large slip. Its failure drives the rupture to propagate into the shallow portion that is likely velocity-strengthening, resulting in significant slip near the trench within a limited area. However, the preferred model suggests that the largest slip in the event occurs near the hypocenter. High-strength patches along the downdip portion of the subducting plane are most effective among several possible factors in generating high-frequency seismic radiations, suggesting the initial strength distribution there is very heterogeneous.