Wedge inelasticity and fully coupled models of dynamic rupture, ocean acoustic waves, and tsunami in the Japan trench: The 2011 Tohoku-Oki earthquake

Abstract

Along-strike variations of sediment thickness and inelastic wedge deformation can significantly affect the variations of near-trench slip, seismic radiation, and tsunamigenesis along the Japan Trench. We present fully coupled models of dynamic rupture, ocean acoustic waves, and tsunami for the 2011 M_W 9.1 Tohoku-Oki earthquake to fully investigate the physics of tsunami generation and radiation fields, by extending a dynamic rupture model with wedge inelasticity (Ma, 2023). The fully coupled models, incorporating ocean compressibility, produce tsunami in good agreement with that from a dispersive shallow-water model, confirming the validity of both models. We show strong radiation of ocean acoustic and seismic waves caused by fast rupture velocity (∼3 km/s) and large near-trench slip south of 39°N, dominated by elastic wedge response. However, north of 39°N where sediment thickens in the northern Japan Trench, the inelastic wedge deformation excites tsunami efficiently with diminishing near-trench slip (<20 m), consistent with differential bathymetry observations, but causes slow rupture velocity (∼850 m/s) and significantly weaker radiation of ocean acoustic and seismic waves. Inelastic wedge deformation thus provides a self-consistent interpretation to both depletion in high-frequency radiation and large tsunami generation in the northern Japan Trench in this earthquake, which may challenge the use of ocean acoustic waves for robust tsunami early warning.