Poster #049, Ground Motions

3D wave propagation simulations of the 2019 M7.1 Ridgecrest, CA, Earthquake

Te-Yang Yeh, & Kim B. Olsen
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Poster Presentation

2021 SCEC Annual Meeting, Poster #049, SCEC Contribution #11626 VIEW PDF
We have performed 3D numerical wave propagation simulations for the July 6 2019 M7.1 Ridgecrest, CA earthquake. The purpose of this study is to use a state-of-the-art 3D simulation tool to better understand how different parts of calculations contribute to variability of broadband ground motions. We present the results of simulations up to 3 Hz with 500 m/s minimum shear wave velocity in a 200 km x 150 km domain focusing on the near-fault regions and the mountainous areas to the Northeast of the Los Angeles Basin. The calculations were carried out on ORNL Summit using the newest version of the GPU-enabled AWP which enables calculations with surface topography on curvilinear grids. We used ve...locity and density information from the SCEC UCVM model CVM-S4.26.M01 with built-in geotechnical layers. The intrinsic attenuation model of Qs=0.1Vs, Qp=2Qs with power-law exponent of 0.6 produced the least biased PGVs throughout our model domain.

We tested kinematic source rupture models inverted from seismic and geodetic data with enhanced high-frequency content, as well as one by the Graves-Pitarka kinematic rupture generator. We find that, as expected, the effects of surface topography increase with frequency, reducing peak ground velocities (PGV) and accelerations (PGA) and prolonging the duration of shaking. Vertical ground motions above 1Hz are enhanced by surface topography by 50% on average while horizontal ground motions are slightly weakened by 20% between 0.1-0.5 Hz. In addition to topographic scattering, we find that small-scale heterogeneities of 5-10% strength add extra scattering wave energy to the vertical ground motions above 1 Hz. Finally, we find that a general underprediction of the PGVs by our simulations at sites where the near-surface velocity structures are not well constrained can be alleviated by incorporating Vs30 information.