Ground Motion Simulations for an M4.2 Aftershock of the Niigata-Chuetsu Earthquake of 2007 Using Large-Scale Wavefield Simulations

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

The aim of this research is to generate realistic ground motions utilizing a physics-based approach with advanced finite difference methods. These simulated ground motions are validated against recorded ground motions. To that end, SW4 code was used for large-scale wavefield simulations and the HPC cluster at University of Nevada Reno was used to overcome computational challenges. The code allows for complex geometries and heterogeneous material properties with realistic boundary and interface conditions, while achieving a 4th order accuracy of the 3D visco-elastic wave equations that are used to model the earthquake.

The site of interest is the widely studied geotechnical downhole array, Service Hall Array (SHA), at Kashiwazaki-Kariwa Nuclear Power Plant (KKNPP) in Japan, and the event simulated is a M4.2 aftershock of the 2007 Niigata-Chuetsu earthquake. This aftershock event was chosen since its epicenter, located in proximity (4 km) to KKNPP, allowed the use of a smaller computational domain and a finer grid to improve the quality of synthetic seismograms. The surface-focused structured mesh refinement (SMR) feature in SW4 allows for a finer grid to accommodate lower compressional and shear wave velocities in the shallow layers. The maximum frequency computed from the synthetic seismograms was 3 Hz.

Recorded data from SHA was utilized to validate the simulated ground motions; acceleration time histories as well as Fourier Amplitude Spectra were compared. Simulations using a Community Velocity Model (CVM) were contrasted with those using a CVM integrated with the site-specific material properties for shallow layers. Comparison of the same with recorded ground motions provided insight into the improvements in synthetic seismograms for a thoroughly studied site.

Presenting Author: Swasti Saxena

Authors