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The Enhancement of Coseismic Slip and Ground Motion Due to the Accretionary Wedge and Sedimentary Layer in the 2011 Tohoku-Oki Earthquake

Session: Physics-Based Earthquake Rupture Modeling and Strong Motion Simulations [Poster]

Type: Poster

Date: 4/22/2021

Presentation Time: 03:45 PM Pacific

Description: 

Low-velocity accretionary wedges and sedimentary layers overlying continental plates are widely observed in the subduction zones where historical large earthquakes (M_w >8.5) have occurred. It was observed that the rupture of the 2011 M_w 9.0 Tohoku-Oki earthquake propagated to the trench with large coseismic slip on the shallow fault, but what caused the huge shallow slip still remains a prominent problem. Here we aim at exploring how the low-velocity structures, accretionary wedge and sedimentary layer, affect the coseismic slip and near-fault ground motions during the 2011 Tohoku-Oki earthquake. Constrained by the observed seafloor deformation, we present a 2-D dynamic rupture model of the 2011 Tohoku-Oki earthquake with an accretionary wedge and a sedimentary layer. Compared to a homogeneous model with the same friction and stress parameters on the fault, we find that the co-existence of the accretionary wedge and sedimentary layer greatly enhances the shallow coseismic slip and amplifies ground accelerations near the accretionary wedge.

We then investigate a plausible scenario of a smaller Tohoku-Oki earthquake when its rupture does not reach the accretionary wedge. The sedimentary layer slightly enhances the coseismic slip while the accretionary wedge has almost no influence for the smaller earthquake scenario, but both structures significantly amplify the ground accelerations on the overriding plate. We suggest that the co-existence of an accretionary wedge and sedimentary layers tend to enhance coseismic slip, but the enhancement effect decreases as the up-dip limit of rupture zones terminates at a larger depth.

Presenting Author: Xian Li

Student Presenter: Yes

Authors