Qian Yao1,2 and Shuo Ma1
1 Department of Geological Sciences, San Diego State University
2 IGPP, Scripps Institute of Oceanography, University of California, San Diego
Signatures of Inelastic Coseismic Wedge Deformation in the Near-Field Tsunami
It was recently proposed that coseismic Coulomb failure in the overriding wedge above a shallow-dipping plate interface significantly affects the tsunami generation and seismic radiation in the shallow subduction zone (Ma, 2012; Ma and Hirakawa, 2013). The inelastic wedge deformation not only induces peak seafloor uplift more landward from the trench, it also explains the slow rupture velocity, depletion in high-frequency radiation, low moment-scaled radiated energy, and small heat flow anomaly across the fault, which are well-documented anomalous characteristics for shallow subduction earthquakes. This mechanism challenges the use of elastic dislocation theory in explaining the coseismic deformation and tsunami data. On-land GPS data have limited resolution to the deformation near the trench, to which near-field tsunami data, however, have probably the best resolving power. Here we simulate the near-field tsunami waveforms by using the time-dependent seafloor displacement fields resulted from 2D elastic and inelastic simulations of dynamic rupture on a 15° dipping fault. The more landward peak uplift in the inelastic model generates earlier tsunami arrivals on shore than the peak uplift at the trench in the elastic model. The timing difference, however, is small in the case of 15° dip because the location of peak uplift differs by only ~20 km between the two models. We expect a more significant timing difference for shallower fault dips, which will be our next step. Another important constraint on the location of peak uplift provided by the tsunami data is the arrival time of reflected phases from the shore.
2013 AGU Annual Meeting