Shallow Crustal Shear Velocity and Vp/Vs Across Southern California: Joint Inversion of Short‐Period Rayleigh Wave Ellipticity, Phase Velocity, and Teleseismic Receiver Functions
Elizabeth M. Berg, Fan‐Chi Lin, Vera Schulte‐Pelkum, Amir Allam, Hongrui Qiu, & Konstantinos GkogkasPublished July 28, 2021, SCEC Contribution #10968
Near-surface seismic velocity structure plays a critical role in the amplification of ground motion during large earthquakes. In particular, the local Vp/Vs ratio strongly influences the amplitude of Rayleigh waves. Previous studies have separately imaged 3D seismic velocity and Vp/Vs ratio at seismogenic depth, but lack regional coverage and/or fail to constrain the shallowest structure. Here, we combine three datasets with complementary sensitivity in a Bayesian joint inversion for shallow crustal shear velocity and near-surface Vp/Vs ratio across Southern California. Receiver functions – including with an apparent delayed initial peak in sedimentary basins, and long considered a nuisance in receiver function imaging studies – highly correlate with short-period Rayleigh wave ellipticity measurements and require the inclusion of a Vp/Vs parameter. The updated model includes near-surface low shear velocity more in line with geotechnical layer estimates, and generally lower than expected Vp/Vs outside the basins suggesting widespread shallow fracturing and/or groundwater undersaturation.
Citation
Berg, E. M., Lin, F., Schulte‐Pelkum, V., Allam, A., Qiu, H., & Gkogkas, K. (2021). Shallow Crustal Shear Velocity and Vp/Vs Across Southern California: Joint Inversion of Short‐Period Rayleigh Wave Ellipticity, Phase Velocity, and Teleseismic Receiver Functions. Geophysical Research Letters, 48(15). doi: 10.1029/2021GL092626.
