SCEC Award Number 20157 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Modeling of the 2019 M7.1 Ridgecrest, CA, Earthquake
Name Organization
Kim Olsen San Diego State University
Other Participants PhD Candidate Te-Yang Yeh
SCEC Priorities 4a, 4b, 4c SCEC Groups GM, CS, CXM
Report Due Date 03/15/2021 Date Report Submitted 04/09/2021
Project Abstract
The purpose of this study is to better understand how different components of the model contribute to variability of broadband ground motions. Toward this goal, we have performed 3D numerical wave propagation simulations for the July 6 2019 M7.1 Ridgecrest, CA earthquake in model domains with horizontal dimensions of 200 km by 300 km and 200 km by 150 km up to 3 Hz with 500 m/s minimum shear wave velocity. The calculations were carried out on ORNL Summit using the GPU-enabled AWP-ODC finite difference code which enables calculations with surface topography on curvilinear grids (O'Reilly et al., 2019). Velocity and density information were taken from the SCEC CVM-S4.26.M01 with built-in geotechnical layers. We tested multi-segment source rupture models inverted from seismic and geodetic data with enhanced high frequency content. We find that, as expected, the effects of surface topography increase with frequency, primarily reducing peak ground velocities (PGV) and increasing durations. The intrinsic attenuation model of Qs=0.1Vs, Qp=2Qs produced the least biased PGVs throughout our model domain.
Intellectual Merit The results of this study help to better understand how different components of the model contribute to the variability of broadband ground motions, including topography, small-scale heterogeneities, Q(f), and the accuracy of the velocity model.
Broader Impacts A better understanding of the effects of different model features is poised to help improve seismic hazard analysis in the future, as well as provide guidance for which model features need to be included as frequencies increase in the models. The funding for this project helped support a PhD student, Te-Yang Yeh.
Exemplary Figure Figure 5. Topographic amplification map and histogram. Green dots outline the trace of the M7.1 event. We compute the RMS PGVs within 0.02 - 3 Hz with and without surface topography (Figure 5). 44% of the stations experience more than 10% reduction in PGV from topographic scattering, whereas only 6% of the domain observes more than 10% PGV amplification. On average, topographic scattering reduces the peak-ground velocity by 8.6% within the model domain. The locations where positive topographic amplifications are observed generally coincide with ridges or crests, which is likely due to focusing effects. Seismic waves are trapped and amplified in the low velocity sediments surrounded by rocks with higher wave speeds. In addition to the effects on amplitudes, we see a 10% increase in duration of velocity waveforms and 60% increase in the duration of acceleration waveforms due to increased scattering occurring at the free surface.