UCLA

The National Seismic Hazard Model Program Steering Committee (NSHM-SC) conducts participatory peer-review during the development of NSHM products, working with the NSHM development team in the U.S. Geological Survey (USGS). This report documents the review processes and outcomes related to the development of NSHM products for application to Puerto Rico and the Virgin Islands (PRVI). The committee consists of nine members who were selected by the USGS, based on expertise and experience. The USGS requested a written report from the NSHM-SC answering the following questions relevant to publication of the 2023 NSHM for PRVI: • Was the National Seismic Hazard Model adequately reviewed? • Did the USGS respond appropriately to the review comments and recommendations? • Is the model suitable for release and to serve as the basis for hazard mitigation? The SC responses to the three main questions are: Was the National Seismic Hazard Model adequately reviewed? The NSHM-SC, and earthquake rupture forecast (ERF) and ground motion characterization (GMC) expert panels called by the NSHM-SC, engaged in several meetings to review components and the complete model between August 2024 and December 2025. The NSHM-SC consensus is that the level of review of the materials provided has been adequate. Did the USGS respond appropriately to the review comments and recommendations? The USGS responded to all NSHM-SC and panel comments and recommendations. USGS adopted most of our recommendations. When not adopted, USGS provided explanations that often indicated that a suggested modification could not be made due to limited time or because adopting the suggestion would break long-standing precedent. Because the panels and the NSHM-SC are advisory in nature, this is acceptable. Is the model suitable for release and to serve as the basis for hazard mitigation? The NSHM-SC considers the 2025 NSHM for PRVI to be suitable for use in building code and similar applications at return periods of 475 years (i.e., corresponding to exceedance probabilities of 10% in 50 years) or longer. The 2025 NSHM for PRVI represents a substantial improvement over the previous NSHM for PRVI developed in 2003, because of the use of better input source characterization models, better ground-motion models, and overall improved computational techniques.