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Shallow Crustal Shear Velocity and Vp/Vs Across Southern California: Joint Inversion of Short-Period Rayleigh Wave Ellipticity, Phase Velocity and Onset of Teleseismic Receiver Functions

Session: Waveform Cross-Correlation-Based Methods in Observational Seismology [Poster]

Type: Poster

Date: 4/21/2021

Presentation Time: 03:45 PM Pacific

Description: 

We use 231 stations across Southern California to jointly constrain Vp/Vs and shear velocities in the near-surface through a Bayesian inversion of three datasets with complementary sensitivities. These datasets include the onset of teleseismic receiver functions, short-period ambient-noise derived Rayleigh phase velocities, and ellipticity dispersions. We fit all three datasets through the inclusion of a Vp/Vs parameter for the near-surface layer, and find strong correlation between short-period Rayleigh-wave ellipticity and apparent onset delay (0-2s) of receiver functions. In particular we fit receiver functions with a delayed initial peak due to sedimentary basin reverberations, which have long been considered a nuisance to deeper imaging studies. Our updated Southern California model includes upper crust to near-surface (<10km) shear velocities, and near-surface Vp/Vs ratios. Our model shows 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. This finding is critical to seismic hazard assessment; local Vp/Vs ratio strongly influences the amplitude of Rayleigh waves to a greater extent than the shallow near-surface Vs alone. In addition to self-consistent shallow constraint and regional coverage, the applied Markov Chain Monte Carlo inversion fully quantifies data sensitivity and uncertainty.

Presenting Author: Elizabeth M. Berg

Student Presenter: Yes

Authors