Impulsive Tsunami and Large Runup Along the Sanriku Coast of Japan Produced by an Inelastic Wedge Deformation Model

Abstract

AbstractDynamic wedge failure produces short‐wavelength seafloor uplift efficiently with diminishing shallow slip on the plate interface, generating impulsive tsunami. For ria coasts with prevalent small‐wavelength bathymetric and geomorphologic features, such as the Sanriku coast of Japan, impulsive tsunami can be amplified to produce large runup. We model tsunami propagation and runup of the 1896 Sanriku tsunami by using the seafloor deformation from dynamic rupture models of Ma and Nie (2019) for a MW 8 earthquake with inelastic wedge deformation. The nonlinear Boussinesq equation is solved by a nested‐grid finite‐difference method with high‐resolution bathymetry data. We show that an inelastic deformation model with extensive wedge failure produces impulsive tsunami similar to those observed offshore the Sanriku coast in the 2011 Tohoku earthquake and generates large runup remarkably consistent with the 1896 Sanriku tsunami. As an alternative to previous models based solely on fault slip, we suggest that the impulsive tsunami and large runup along the Sanriku coast observed in the 2011 Tohoku earthquake can be explained by inelastic wedge deformation north of 38.5°N.