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April 5, 2026Earthquake Spectra3 citationsOpen Access

The 2025 Puerto Rico and Virgin Islands U.S. National Seismic Hazard Model Update: Ground Motion Model Selection and Comparison

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KWK. WithersMMMorgan P. MoschettiBAB. Aagaard

Key Points

  • This research aims to identify and validate ground motion models for the updated seismic hazard assessment in Puerto Rico and the U.S. Virgin Islands.
  • Evaluated global ground motion models suitable for active crustal and subduction earthquakes.
  • Incorporated local site response analyses from ground motion records to adjust models.
  • Combined unadjusted and regionally corrected models into a robust median ground motion prediction framework.
  • Used a logic tree to address epistemic uncertainty and variations in parameters like magnitude and distance.
  • New models generally predict lower ground motions compared to those used in the 2003 update.
  • Increased aleatory variability and epistemic uncertainty raise hazard levels significantly.
  • Probabilistic ground motion estimates can vary by 10%-20% at the 2% in 50 years exceedance level due to updated models.

Abstract

We evaluate, select, and describe the ground‐motion models (GMMs) used in the 2025 update of the U.S. National Seismic Hazard Model (NSHM) for Puerto Rico and the U.S. Virgin Islands (PRVI). We identify the most appropriate models that align with GMM selection criteria for use in the PRVI region to improve the accuracy of seismic hazard assessments. The update incorporates globally applicable GMMs suited for the active crustal and subduction earthquakes in the region. We include region‐specific adjustments to these GMMs derived from local site response analyses derived from ground motion records. The unadjusted and regionally‐corrected GMMs are combined to create a robust model for predicting median ground motion. The model integrates epistemic uncertainty through a median ground motion logic tree that accounts for variations in magnitude and distance. This study compares the GMMs selected for the 2025 PRVI NSHM, including both as‐provided and regionally adjusted NGA‐West2 and NGA‐Subduction models, with those used in the 2003 PRVI NSHM. We evaluate how changes in model selection, weighting, aleatory variability, and epistemic uncertainty influence seismic hazard estimates. Trends with distance, magnitude, and spectral period are analyzed to evaluate how the scaling behavior of the newer GMMs differs from that of earlier models. Relative to the GMMs used in the 2003 NSHM for this region, the 2025 models generally predict lower ground motions. Comparisons with additional GMMs indicate that the adjustments applied for PRVI are consistent with regional‐specific modifications developed elsewhere globally. The increase in aleatory variability and epistemic uncertainty in the 2025 update results in a notable increase in hazard levels from these wider uncertainty bounds. These changes can result in as much as a 10%–20% variation in probabilistic ground motion at the 2% in 50 years exceedance level for hazard maps computed across the region for representative site classes and periods.

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Cite This Study

Withers et al. (2026) studied this question.

synapsesocial.com/papers/69d1fdbfa79560c99a0a3f7dhttps://doi.org/10.1002/esp4.70059
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