Adjusting Central and Eastern United States ground-motion models for use in the Coastal Plain considering the sediment thickness

Abstract

This study aims to develop adjustment factors for ground-motion models such as Pezeshk et al., which were developed for regions outside the Coastal Plain to be used for sites within the Coastal Plain region. The adjustment factors developed are a function of sediment thickness and rupture distance $R_{\mathrm{rup}}$ in the Coastal Plain region. We use the newly developed sediment thickness contour maps by Boyd et al. Also, the adjustment factors are developed using a combined data set, which consists of the Next Generation Attenuation (NGA)-East original data set, the data set from Chapman and Guo, and the newly compiled and verified data set by Thompson et al. We calculate residuals by taking the difference between the logarithms of the observed data and those predicted by the Pezeshk et al. ground-motion model (GMM), considering the site amplification model of Stewart et al. and utilizing the combined data set. This model is applicable for $R_{\mathrm{rup}}$ as far as 1000 km. We perform residual analyses using a mixed-effects regression to partition the total residuals into between-event and within-event components. To develop the correction factors for stations within the Coastal Plain region, we fit the within-event residuals to an equation that is a function of sediment thickness and $R_{\mathrm{rup}}$ . The results indicate that for stations within the Coastal Plain region, for most periods, the residual trend has been eliminated (with respect to sediment thickness, $R_{\mathrm{rup}}$ , and time-averaged shear wave velocity in the first 30 m under the surface, V _S30 ) using the proposed adjustment factors. The results of this study can be utilized in seismic hazard and risk analyses for sites within the Coastal Plain.