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Ambient Noise Tomography Across the 2022 Los Angeles Basin Nodal Array

A detailed 3D model of the Los Angeles Basin (LAB) is crucial for earthquake hazard assessment in the Los Angeles metropolitan area. In 2022, a month-long dense nodal geophone array was deployed in the LAB, consisting of a 185-station distributed sub-array and two ~50-station linear sub-arrays. In this presentation, we show the result of applying ambient noise tomography to study the LAB structure across the nodal array. We calculate multi-component ambient noise cross-correlations using both nodal and regional broadband stations. We measure Rayleigh wave horizontal-to-vertical amplitude (H/V) ratios between 5-9 s period across the nodal array after off-great-circle correction and compare them to the predictions based on SCEC Community Velocity Model S4.26 (CVM). Clear discrepancies are observed near the Central and the West Coast Basins, where the depth velocity gradients of the CVM are likely too low and too high, respectively. We also perform beamforming to determine fundamental (2-13 s period) and higher-mode (2-4.5 s period) phase velocities and H/V ratios across the dense linear sub-arrays. For each location, we jointly invert for multi-mode phase velocities and H/V ratios to get a 1-D Vs model, extending from the surface to a depth of 10 km. All 1-D models are combined to obtain the final 2-D Vs models, which we compared with CVM. In general, our model exhibits a stronger vertical velocity gradient in the top 2 km than the CVM, suggesting that the CVM may underpredict ground motions in earthquake simulations. We will also show and discuss the preliminary 3D LAB model.

Session: Generating, Calibrating and Validating Multi-Scale Seismic Velocity Models - I

Type: Oral

Room: Ballroom C

Date: 4/17/2026

Presentation Time: 08:45 AM (local time)

Presenting Author: Fan-Chi Lin

Student Presenter: No

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