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

Session: Exploring Rupture Dynamics and Seismic Wave Propagation Along Complex Fault Systems II

Type: Oral

Date: 4/20/2021

Presentation Time: 10:00 AM Pacific

Description: 

The Sanriku coast of Japan was hit by several of the worst tsunamis in the recorded history. In the 2011 Tohoku tsunami the largest tsunami heights (up to 40 m) were observed on the Sanriku coast, more than 100 km north of the epicenter. The tsunami heights on the Sanriku coast were consistently 2 – 3 times larger than in the south. The 1896 Sanriku earthquake (~M_W 8) also generated similar tsunami heights on the Sanriku coast as in the 2011 M_W 9.0 Tohoku earthquake. In order to explain the large 2011 Tohoku tsunami heights, elastic dislocation models require large trench slip (up to 36 m) more than 100 km north of the epicenter, which is, however, inconsistent with the differential bathymetry data (Fujiwara et al., 2017). Ma and Nie (2019) showed that inelastic wedge deformation due to thick sediments in the region can efficiently generate seafloor uplift while reducing near-trench slip, which is more consistent with the observations. Here we simulate tsunami propagation of the 1896 Sanriku earthquake by using the seafloor uplift of Ma and Nie (2019) and high-resolution bathymetry data. We show that the short-wavelength seafloor uplift by inelastic wedge deformation produces impulsive tsunami signals (such as those recorded at TM1, TM2 and three Iwate GPS wave gauges in the 2011 Tohoku tsunami) and generates large runup consistent with the observations of the 1896 Sanriku tsunami.

Presenting Author: Yue Du

Student Presenter: Yes

Authors