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Abstract We image the shallow structure across the East Bench segment of the Wasatch fault system in Salt Lake City using ambient noise recorded by a month-long temporary linear seismic array of 32 stations. We first extract Rayleigh-wave signals between 0.4 and 1.1 s period using noise cross correlation. We then apply double beamforming to enhance coherent cross-correlation signals and at the same time measure frequency-dependent phase velocities across the array. For each location, based on available dispersion measurements, we perform an uncertainty-weighted least-squares inversion to obtain a 1D VS model from the surface to 400 m depth. We put all piece-wise continuous 1D models together to construct the final 2D VS model. The model reveals high velocities to the east of the Pleistocene Lake Bonneville shoreline reflecting thinner sediments and low velocities particularly in the top 200 m to the west corresponding to the Salt Lake basin sediments. In addition, there is an ∼400-m-wide low-velocity zone that narrows with depth adjacent to the surface trace of the East Bench fault, which we interpret as a fault-related damage zone. The damage zone is asymmetric, wider on the hanging wall (western) side and with greater velocity reduction. These results provide important constraints on normal-fault earthquake mechanics, Wasatch fault earthquake behavior, and urban seismic hazard in Salt Lake City. 

Near‐surface seismic velocity structure plays a critical role in ground motion amplification 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.