Shallow crustal structure of Southern California by jointly inverting surface wave phase velocity, Rayleigh wave ellipticity, and Receiver Functions

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

Published August 16, 2021, SCEC Contribution #11575, 2021 SCEC Annual Meeting Poster #013

An accurate and high-resolution shallow crustal model is important for understanding ground motion amplification and hence regional seismic hazard. In this study we present a new shear velocity (Vs) crustal model of the Southern California region by jointly inverting ambient noise derived surface wave phase velocity, Rayleigh wave ellipticity, and teleseismic receiver functions under a Bayesian framework. In particular, we show that both the initial peak of receiver functions and short period Rayleigh wave ellipticity are extremely sensitive to shallow crustal structure. The complementary sensitivities of the measurements allow us to resolve not only shallow crustal Vs structure but also near-surface Vp/Vs ratios. The updated model in general has slow shallow shear velocities in good agreement with previous geotechnical layer estimates. The unexpectedly low Vp/Vs ratios outside of the major sedimentary basins, on the other hand, likely indicate extensive shallow fracturing and/or groundwater undersaturation. To further refine our model, we add Love wave phase velocities to the joint inversions. Preliminary results suggest that an isotropic model can adequately fit the data in the region except for deep sedimentary basins where short period Rayleigh and Love wave phase velocities display fundamental disagreement; this is potentially due to significant radial anisotropy. In addition to incorporating radial anisotropy in the inversion, we are also in the process of validating the short period measurements based on regional earthquake data. Our approach underscores the improvement in model constraints gained by combining multiple datasets in a Bayesian framework.

Citation
Gkogkas, K., Berg, E., Lin, F., Schulte-Pelkum, V., Allam, A. A., & Qiu, H. (2021, 08). Shallow crustal structure of Southern California by jointly inverting surface wave phase velocity, Rayleigh wave ellipticity, and Receiver Functions. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
SCEC Community Models (CXM)