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Validation of Shallow Crustal Structure in Northern California and Community Velocity Model Validation Using Ambient-noise-derived Rayleigh Wave Ellipticity and Receiver Functions

Description: 

Northern California has numerous active faults, including the Hayward Fault near the San Francisco Bay Area, which is prone to generating a devastating large-magnitude earthquake. An accurate three-dimensional (3D) seismic velocity model is an important component for accurately predicting ground motions upon realistic earthquake scenarios. In Northern California, the regional Northern California USGS seismic velocity model (USGS_SVM) was constructed for this purpose, and it has been iteratively refined using 3D ground-motion simulations, body wave travel times, and surface wave dispersion measurements to minimize discrepancies between model predictions and observations. Recent studies indicate that Rayleigh wave ellipticities (H/Vs) from ambient noise cross-correlations and a time delay of the first peak of receiver functions (RFs) could provide additional constraints on the shallow crustal structure that can further improve the existing velocity models.

We compute nine-component ambient noise cross-correlations using data from a combination of permanent and temporary stations in Northern California. This includes 200 broadband stations from permanent networks during January to March 2024 and temporary broadband and dense geophone arrays deployed during various time periods. Rayleigh wave H/V values are measured at periods of 6–26 s, producing period-dependent H/V maps. The maps highlight higher H/Vs in the Central Valley and Coastal Ranges and lower values in the Sierra Nevada and northern regions like Clear Lake. RFs, derived from teleseismic earthquake data collected by broadband and short-period stations available during 2014–2024 reveal significantly large first-peak delay times in the Central Valley and correlate well with H/V observations. Our comparisons of H/V and RF results with USGS_SVM predictions identify key discrepancies and areas for refinement, specifically in areas of the San Francisco bay and Mendocino Junction where observations suggest higher values to be considered. We will also present preliminary seismic velocity models by joint inversion of H/V and RF measurements.

Session: Accuracy and Variability of Physics-based Ground Motion Modeling [Poster]

Type: Poster

Date: 4/15/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Gabriela

Student Presenter: Yes

Invited Presentation: 

Poster Number: 91

Authors