Validating and improving community velocity models using Rayleigh wave ellipticity

Fan-Chi Lin, HyeJeong Kim, Konstantinos Gkogkas, Gabriela A. Zaldivar Andrade, Robert W. Clayton, & Taka'aki Taira

Submitted September 7, 2025, SCEC Contribution #14618, 2025 SCEC Annual Meeting Poster #TBD

Accurate 3D crustal velocity models are essential for realistic earthquake ground motion simulations and seismic hazard assessments. Models constructed from seismic traveltimes, whether from earthquakes or noise cross-correlations, often lose sensitivity in the upper few kilometers of the crust, a depth range that is particularly important for assessing ground motion amplification. Other microtremor-based approaches, such as HVSR, SPAC, and MASW, primarily target near-surface velocities and are difficult to scale up for regional studies.

Rayleigh wave ellipticity, or the horizontal-to-vertical (H/V) amplitude ratio, can be measured at seismic stations using multi-component noise cross-correlations and is especially sensitive to shallow crustal structure. Using data from regional seismic networks and temporary array deployments, the technic can be applied at regional scales to fill in the missing constraints in the upper few kilometers. In this presentation, I will discuss results from our recent SCEC projects to measure Rayleigh wave H/V ratios across California. We find that H/V ratios predicted by community velocity models (CVMs) in sedimentary basins often deviate from our observations, revealing potential weaknesses in the CVMs. Example 1D inversions will be shown to illustrate how these models can be improved.

Key Words
CVM, tomography, ambient noise

Citation
Lin, F., Kim, H., Gkogkas, K., Zaldivar Andrade, G. A., Clayton, R. W., & Taira, T. (2025, 09). Validating and improving community velocity models using Rayleigh wave ellipticity. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology