Group A, Poster #167, Ground Motions (GM)

Application for CVMs for NGA-West3 Project

Rashid Shams, Sajan K C, Tristan E. Buckreis, Scott J. Brandenberg, Jonathan P. Stewart, & Chukwuebuka C. Nweke
Poster Image: 

Poster Presentation

2024 SCEC Annual Meeting, Poster #167, SCEC Contribution #13836 VIEW PDF
The Next Generation Attenuation (NGA)-West3 project aims to produce a robust database
(Buckreis et al. 2024) that will facilitate the development of state-of-the-art ground motion
models (GMMs). These GMMs will provide improved characterization of seismic hazards,
particularly for geologic features such as sedimentary basins that lead to complex site
response effects. A critical component to achieve this outcome involves the application of
Community Velocity Models (CVMs) to estimate the depths to 1.0 km/s and 2.5 km/s shear
wave velocity iso-surfaces (basin depths: z 1 & z 2.5 ).

There are CVMs for many regions across the glob...e. For the shallow crustal regions of the
western U.S., this includes the SCEC (CVM-S4) and Harvard (CVM-H) velocity models for
southern California, the San Francisco Bay Area (SFCVM) velocity model for northern
California, the Wasatch Front velocity model for Central-Northern Utah, and the National
Crustal Model that covers the entire U.S. These velocity models are queried across their
domains to estimate basin depths at ground motion recording locations. In the application of
these models, we have encountered several difficulties for which we hope to engage in
discussions with stakeholders at 2024-SCEC Meeting:

1. There can be substantial differences between models for the same region, which is an
issue in Southern California
2. There can be appreciable differences between different versions of the same model, a
particularly acute example of which is CVM-S4 in Imperial Valley
3. There are conditions for which the models do not produce reliable results, such as
outside the domains of sedimentary basins in southern California
4. Physically unrealistic results are provided in some cases, such as depth to the 1.0 km/s
iso-surface = 0 for V S30 < 1.0 km/s sites.
5. There can be issues at the boundaries when transitioning from one model to another
due to differences in resolution amongst the CVMs.

We are currently working through a process to resolve these issues, aided by comparisons of
CVM-derived basin depths with collocated values from measured velocity profiles. The
intended outcome is to provide a defensible and repeatable basis for assigning depths in
basin and non-basin environments and their uncertainties. At SCEC-2024, we hope to engage
in constructive discussions with CVM developers to develop consensus around these issues.
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Citation: Shams, R., K C, S., Buckreis, T. E., Brandenberg, S. J., Stewart, J. P., & Nweke, C. C. (2024, 09). Application for CVMs for NGA-West3 Project. Poster Presentation at 2024 SCEC Annual Meeting.
Keywords: NGAWest3, Community Velocity Models (CVMs)
Relevant SCEC Themes:
Improving Observations and Closing Data Gaps
Advanced Modeling Frameworks
Outreach and Community Engagement