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 Berg, Fan-Chi Lin, Amir A. Allam, Vera Schulte-Pelkum, Hongrui Qiu, & Konstantinos Gkogkas

Submitted 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., Lin, F., Allam, A. A., Schulte-Pelkum, V., 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, (submitted).