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Geologically Informed Non-ergodic Site Effects Model for California Enhanced With Geotechnical Measurements

Description: 

This work presents a non-ergodic site term model for California for use with the Boore et al. (2014) (BSSA14) NGA-West2 ground-motion model. The developed model uses continuous geospatial parameters, along with correction factors for geotechnical measurements (HVSR and V_S30) where available. Recent growth in ground-motion databases has enabled more accurate spatial quantification of repeatable site effects on ground-motion intensity. This work uses recordings from 3,099 stations in the Ji et al. (2022) DesignSafe database paired with geospatial variables (e.g., elevation, soil thickness, and surficial geology). These geospatial parameters serve as primary site terms, offering an alternative to proxy-based V_S30 and Z_1.0. Mixed-effects regression is performed using the geospatial explanatory variables to estimate site response (derived from the BSSA14 site terms and residuals) for PGA, PGV, and PSA at 21 spectral periods. Compared to V_S30-based site terms, the non-ergodic geospatial site terms are found to reduce inter-site variability. The reduction is most significant (an average of 6.6%) when the novel regional geologic unit site parameter (defined by surficial geology and geomorphic province) is used. Correction factors are then developed using HVSR-derived parameters and V_S30 for sites where these measurements are available to further reduce inter-site variability at the sites with site-specific seismic characterizations. We demonstrate the benefit of using HVSR, an inexpensive geotechnical measurement, to enhance ground-motion models by analyzing multiple HVSR parameters (from both earthquake HVSR and microtremor HVSR) and the categorical classification of sites with clear HVSR peaks and those without. The addition of geotechnical correction factors further reduces the inter-site variability by 5.6% using HVSR, 4.5% using V_S30, and 9.9% using both sets of data. The development of a non-ergodic site term for use in California using geospatial variables highlights the predictive power of continuously available non-proxy-based parameters and accounts for their impacts on ground motion intensity.

Session: Station Installations and Site Conditions, a Quest for Improved Strong Motion Database - II

Type: Oral

Date: 4/16/2025

Presentation Time: 04:30 PM (local time)

Presenting Author: Maggie

Student Presenter: Yes

Invited Presentation: Yes

Poster Number:

Authors