Comparisons of VS30 values from single station earthquake-based horizontal-to-vertical-spectral-ratios against non-invasive surface array-based site characterization methods

Alan Yong, Tara A. Nye, Fumiaki Nagashima, Hiroshi Kawase, Koichi Hayashi, Kenneth S. Hudson, & Antony Martin

Published September 8, 2024, SCEC Contribution #13955, 2024 SCEC Annual Meeting Poster #178

We explore the feasibility of using data directly recorded by earthquake network monitoring stations and the inversion technique of Nagashima et al. (2014) on earthquake-based horizontal-to-vertical spectral ratios (eHVSR) to model the shear wave velocity (VS) profiles and calculate the time-averaged VS of the upper 30 meters (VS30). VS30 is commonly used as input for ground-motion models (GMMs) to account for seismic site effects. Standard in-situ methods for calculating VS30 values, including invasive downhole and non-invasive surface array-based methods, can be expensive and sometimes impractical. For 11 stations sited in the Anza and Imperial Valley region of southern California, we assess their eHVSR-based VS30 against VS30 previously estimated from non-invasive methods (Yong et al., 2013, aka: Y13) and find that eHVSR-based VS30 can vary quite significantly (factor of 1.1–1.4) from VS30 estimated by Y13. We nevertheless observe that site residuals computed between observed peak ground acceleration and peak ground velocity estimates from the Boore et al. (2014) GMM, as conditioned by Y13 VS30 estimates and eHVSR-based VS30 values, show insignificant variations in standard deviation (0.51 and 0.64, respectively). The differences between Y13 VS30-based site residuals and eHVSR-based site residuals also does not appear to correlate with differences in VS30 values. Although our preliminary results demonstrate that the method used to obtain VS30 does not significantly affect the resulting ground-motion distribution, a larger dataset will be necessary for developing a robust predictive approach.

Key Words
VS30, single station, eHVSR, site characterization

Citation
Yong, A., Nye, T. A., Nagashima, F., Kawase, H., Hayashi, K., Hudson, K. S., & Martin, A. (2024, 09). Comparisons of VS30 values from single station earthquake-based horizontal-to-vertical-spectral-ratios against non-invasive surface array-based site characterization methods. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motions (GM)