Adjustment for the Gulf Coast and Atlantic Coastal Plain Region Considering Path Terms and Site Terms With Respect to Rupture Distance and Sediment Thickness for the Median NGA‐East Ground‐Motion Characterization

This article presents a study aimed at deriving adjustment factors tailored for the median of the NGA‐East ground‐motion models (GMMs), specifically targeting regions within the Gulf Coast and the Atlantic Coastal Plain. The adjustment factors are formulated based on sediment thickness and R rup within these regions, known as the Coastal Plains. This research utilizes sediment thickness contour maps provided in another study.Residuals are computed by subtracting the natural logarithms of the observed data from those predicted by the median of the NGA‐East GMM and using a comprehensive dataset. This dataset combines the NGA‐East dataset, the Chapman and Guo dataset, and the newly compiled and verified dataset by USGS. Residual analyses are conducted through mixed‐effects regression to segregate total residuals into between‐event and within‐event components. We regress the within‐event residuals using a functional form incorporating sediment thickness and rupture distance to derive correction or adjustment factors for stations located within the Coastal Plains. Results suggest that, for stations within the Coastal Plains, the residual trend has largely been mitigated across most periods concerning site and path terms using the proposed adjustment factors. The results of this study hold applicability in seismic hazard and risk assessments for sites located within the Coastal Plains.