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Non-ergodic Site Model for Ground Motion Analysis: Incorporating Regionalization, Kappa and Basin Effects

Description: 

In this work, we present a linear site model developed using the NGA-West 3 database for Western United States including California, Nevada, and Utah. The site model is derived from the site-to-site residuals of the Fourier Amplitude Spectrum (FAS), calculated using an updated ground motion models (GMM) developed for the NGA-West 3 database. Our site model consists of four main components: (1) Kappa Model: This model is based on site-specific kappa values derived within the ground motion model. We developed a map-based kappa model by combining a kriging model and a geology-informed model, weighted inversely by variance. The map gives more weight to station data in areas close to stations and relies more on the mean model from the geology-based approach in areas farther from stations. (2) Regionalization: We implemented a multi-scale regionalization approach, with each sub-region applying its own correction factor. For areas with dense data coverage, such as the coastal range of California, the regionalization is based on detailed surficial geological units. For less densely sampled areas, physiographic divisions are utilized, providing a refined model where data is abundant while extending coverage across the entire U.S. (3) Basin Model: Basin stations are identified using high-resolution topographic data, and additional corrections are applied to account for basin size. (4) Geotechnical Approach: We incorporated geotechnical parameters using mixed-effect regression, including V_s30​, Z_1.0 and Z_2.5​, where measurements are available, to further refine the model.

This non-ergodic site model combines traditional geotechnical approaches with geospatial and geological information, such as topography, physiography, and surficial geology. These additional datasets are highly reliable, well-distributed, and readily accessible resulting in a spatially continuous site term for ground motion models in the Western United States. The resulting model significantly reduces site-to-site variability and will be published as a component of the NGA-West 3 project.

Session: Challenges and Opportunities in Constraining Ground-motion Models from Physics-based Ground-motion Simulations - III

Type: Oral

Date: 4/17/2025

Presentation Time: 02:30 PM (local time)

Presenting Author: Shiying

Student Presenter: No

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