Group B, Poster #098, Fault and Rupture Mechanics (FARM)

Wedge Plasticity and a Minimalist Dynamic Rupture Model for the 2011 MW 9.1 Tohoku-Oki Earthquake and Tsunami

Shuo Ma
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Poster Presentation

2023 SCEC Annual Meeting, Poster #098, SCEC Contribution #12760 VIEW PDF
One crucial yet unanswered question about the 2011 Tohoku-Oki earthquake and tsunami is what generated the largest tsunami (up to 40 m) along the Sanriku coast north of 39°N without large slip near the trench. A minimalist dynamic rupture model with wedge plasticity is presented to address this issue. The model incorporates the important variation of sediment thickness along the Japan Trench into the Japan Integrated Velocity Structure Model (JIVSM). By revising a heterogeneous stress drop model of Kubota et al. (2022) the dynamic rupture model with a standard rate-and-state friction law produces a remarkable fit with minimum model tuning to the GPS, tsunami, and differential bathymetry data... (within data uncertainties). The rupture is driven by a large patch of stress drop up to ~10 MPa near the hypocenter with significantly smaller stress drop (< 3 MPa) in the upper ~10 km. The largest shallow slip reaches 75.67 m close to the trench north of hypocenter, caused by the free surface, shallowly dipping fault geometry, and increasing sediment thickness. The northward rupture reaches ~39.8°N, which is dominated by inelastic deformation of thick wedge sediments, giving rise to slow rupture velocity (~850 m/s), diminishing shallow slip, and efficient seafloor uplift. The short-wavelength inelastic uplift produces impulsive tsunami remarkably consistent with the observations off the Sanriku coast. Thus, wedge plasticity and variation of sediment thickness along the Japan Trench provides a self-consistent interpretation to the along-strike variation of near-trench slip and anomalous tsunami generation in the northern Japan Trench in this earthquake.