Ground Motion Response Study of Urban Los Angeles following the 2019 Ridgecrest Earthquake Sequence

Filippos Filippitzis, Monica D. Kohler, Thomas H. Heaton, Robert W. Graves, Robert W. Clayton, Richard Guy, Julian Bunn, & Kanianthra Chandy

Published August 14, 2020, SCEC Contribution #10638, 2020 SCEC Annual Meeting Poster #071 (PDF)

We study ground motion response in urban Los Angeles during the two largest events (M7.1 & M6.4) of the 2019 Ridgecrest earthquake sequence, using recordings from multiple regional seismic networks as well as a subset of stations from the much denser Community Seismic Network (CSN - csn.caltech.edu), which is a dense 700-station, strong-motion network permanently installed in the area of urban Los Angeles. The response spectral (pseudo) accelerations (SA) for a selection of periods of engineering significance are calculated. Significant SA amplification is present and reproducible between the two events. In general, the SA is coherent across the basin at periods greater than 4 seconds, shows significant amplification in the sedimentary basin, but the largest amplifications are not near the deepest part of the basin. At shorter periods the motions are stronger and less spatially coherent, indicating a high-level of scattering at the kilometer scale length. We examine possible correlations of the computed SA with two common geotechnical parameters: basement depth and Vs30, and find no significant correlation for the 1-s period, while a correlation appears and gets stronger for longer periods. In the second part of the study, we examine the performance of 3D finite difference simulations in estimating the ground motions and SA for the largest event of the Ridgecrest earthquake sequence, using the two different Southern California Earthquake Center 3D Community Velocity Models: CVM-S and CVM-H. Overall, the simulations match the mean amplitude and variance of the observations reasonably well. However, they are not able to reproduce the exact locations of the maximum SAs.

Key Words
Earthquake ground motions, 2019 Ridgecrest earthquake sequence, Community Seismic Network, Model Predictions

Citation
Filippitzis, F., Kohler, M. D., Heaton, T. H., Graves, R. W., Clayton, R. W., Guy, R., Bunn, J., & Chandy, K. (2020, 08). Ground Motion Response Study of Urban Los Angeles following the 2019 Ridgecrest Earthquake Sequence. Poster Presentation at 2020 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology