Numerical Simulation Study of Potential Megathrust Event Along the Southernmost Ryukyu Trench

Over the past one hundred years, several big earthquakes with magnitude larger than 9 had occurred along the subduction zones. For example, the 1960 Chile earthquake (M 9.5), the 2004 Sumatra-Andaman earthquake (M 9.3), and the 2011 Tohoku earthquake (M 9.0). In this study, we focus on the southernmost Ryukyu Trench offshore northeastern Taiwan where the Philippine Sea Plate subducts beneath the Eurasian Plate at a rate of 80-85 mm/yr. Once a megathrust event hit this area, the ground shaking and tsunami would cause extreme disaster in northern Taiwan, especially the Taipei metropolitan area. Interseismic GPS data in northeast Taiwan shows a pattern of strain accumulation suggests that the maximum likely magnitude of a potential future large earthquake along the southernmost Ryukyu subduction zone is probably about Mw 8.7. In order to evaluate the influence of this potential megathrust event, we analyze the ShakeMap and ShakeMovie from different rupture scenarios based upon spectral-element method. Tsunami simulations based on coseismic deformations of seabed are carried out to evaluate the amplitudes of tsunami along the coastal areas of Taiwan. In addition, we apply the interseismic GPS data to invert the source slip pattern on a 3D subduction zone. We also discuss the influence of dynamic rupture process on the seabed coseismic deformation and tsunami generation. These numerical simulation results can provide physics-based information of megathrust earthquake scenario for the government and emergency response agency to take the appropriate action before the really big one occurs.