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Geologically Informed Non-ergodic Site Effects Model for the Western US Outside of California

Description: 

This work presents a non-ergodic site term model for the Western U.S. outside of California for use with the Boore et al. (2014) (BSSA14) NGA-West2 ground-motion model. This work builds on a similar effort undertaken for California. The developed model uses continuous geospatial parameters to predict the site term, and quantifies repeatable site effects on ground motion intensity in a continuous spatial manner. This approach results in a non-ergodic site term without the need for interpolation, which is beneficial due to the limited spatial coverage of seismic stations in the Western U.S. outside of California. This project uses the Ji et al. (2022) DesignSafe database containing over 14,000 recordings at 669 stations across Oregon, Utah, Nevada, and Arizona, and the Moschetti et al. (2021) database for Utah earthquakes from 2010 to 2020 that contains over 3,000 recordings at 201 stations. Each station is paired with its corresponding geospatial parameters (e.g., elevation, soil thickness, surficial geology, and geomorphic province), which serve as the primary variables in the site terms, offering an alternative to proxy-based variables V_S30 and Z_1.0. When site-specific measurements are available, a V_S30-based correction is added to further reduce the ground-motion residuals. Mixed-effects regression is performed using geospatial explanatory variables to estimate site response (derived from the BSSA14 site terms and residuals) for PGA, PGV, and PSA at 21 periods. Compared to the conventional V_S30-based site terms, the non-ergodic geospatial site terms reduce the inter-site variability. The development of a non-ergodic site term for use in the Western U.S. outside of California highlights the predictive power of continuously available non-proxy-based parameters and accounts for their impact on ground motion intensity. Furthermore, this work demonstrates how we can leverage geologic data in areas of low station density to accurately predict site terms, and how a V_S30 correction can be applied to further reduce the ground motion residuals where site-specific measurements are available.

Session: Station Installations and Site Conditions, a Quest for Improved Strong Motion Database [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Maggie

Student Presenter: Yes

Invited Presentation: 

Poster Number: 64

Authors