Wedge Plasticity and Fully Coupled Simulations of Dynamic Rupture and Tsunami in the Cascadia Subduction Zone.

Inelastic wedge deformation likely plays an important role in the generation of tsunami and ocean acoustic waves in accretionary subduction margins. In an elastic dislocation model, whether or not the fault breaks the trench has a significant effect on seafloor deformation and resulting tsunami. However, this boundary condition is less important when significant inelastic deformation in the overriding wedge occurs, because large seafloor uplift can occur with little or no slip at the trench. Here we incorporate wedge plasticity in fully coupled dynamic rupture and tsunami simulations for a buried fault in the Cascadia subduction zone with realistic fault geometry, bathymetry, and velocity structure. A linearized Eulerian approach is verified and used to simulate gravity waves in the ocean. Our coupled models show that the inelastic deformation of wedge sediments can significantly contribute to seafloor uplift, producing tsunami heights at least twice as large as in purely elastic simulations, whilst generating weaker ocean acoustic and seismic waves. Inelastic wedge deformation is therefore an important mechanism to consider in tsunami hazard assessment in the Cascadia subduction zone. These results have important implications for tsunami generation and early warning in accretionary and other sediment‐filled margins worldwide. Plain Language Summary: Thick sediments in accretionary plate margins, such as the Cascadia subduction zone, can significantly affect tsunamigenesis and excitation of ocean acoustic and seismic waves. Due to weak strength wedge sediments can fail inelastically under dynamic stresses during an earthquake. Our fully coupled models of earthquake rupture and tsunami in the Cascadia subduction zone show that the inelastic deformation of wedge sediments produces tsunami several times larger than in purely elastic deformation models. Meanwhile, inelastic deformation reduces the excitation of most ocean acoustic and seismic waves, which poses challenges in using these waves for tsunami early warning. Inelastic wedge deformation should be incorporated into more accurate tsunami hazard assessment in the Cascadia subduction zone and other sediment‐filled margins worldwide. Key Points: Inelastic wedge deformation can significantly contribute to tsunamigenesis in the Cascadia subduction zoneA linearized Eulerian approach for modeling ocean gravity waves is verified by a semi‐analytical approachInelastic wedge deformation significantly reduces excitation of ocean acoustic and seismic waves [ABSTRACT FROM AUTHOR]