Characterized Fault Model for Prediction of Long-Period Ground Motions Containing Permanent Displacement in the Near-Fault Region

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

A series of M6-7 earthquakes occurred from April 14 to 16 in 2016 in the Kumamoto prefecture of the Kyushu Island, Japan. The main-shock (Mw7.0, 2016/4/16) generated the extensive surface faulting, and the displacements at Mashiki City and Nishihara Village show clearly permanent displacement. We propose a new procedure for evaluating the parameters of characterized fault model for predicting long-period ground motions containing permanent displacement in the near-fault region.

First, we construct a characterized source model (Model-01) for the main shock based on Irikura recipe. Besides, we expand the Irikura recipe for shallower region than the seismogenic layer. We recommend the regularized Yoffe-type slip velocity functions by Tinti et al. (2005) for shallower region than the seismogenic layer. We evaluate the relation of the slip and the parameters of the regularized Yoffe function from collected source fault models based on the waveform inversion of strong motion data.

Next, we simulate observation records at KiK-net Mashiki and Nishihara village using this source fault models by the theoretical method in the period over 1s. Model-01 underestimate the observation waveforms of velocity and displacement at Nishihara village. The radiation amplitude patterns of S-waves from the seismogenic layer are small in the near-fault region (<1km), that is one of the reasons for the underestimate.

Finally, we construct two source models, Model-02 with large slip and short slip duration for shallower region than the seismogenic layer and Model-03 with the additional fault plane. The additional fault plane in Model-03 is Idenoguchi fault located 2km southeast of main fault. By and large, synthetic waveforms produced with these two models waveforms are in much closer agreement with observed waveforms. We conclude that the Model-03 can describe the actual phenomenon best. This result suggests that geometric shape of the source fault model is important for predicting long-period ground motions containing permanent displacement in the near-fault region.

Presenting Author: Shinya Tanaka

Authors