Site and Basin Effects in the Central and Eastern US: City- and State-Scale Evaluations in Memphis, New York City, and Massachusetts

Many cities in the central and eastern United States (CEUS) are located in sedimentary basins with strong potential for soil amplification and earthquake-induced damage. In this study, we examine city-scale site response in two cities that reside within basin structures: Memphis, Tennessee, and New York City, NY, and we also perform a state-scale site response evaluation throughout the entirety of Massachusetts, which encompasses several sedimentary basins. We perform theoretical linear one-dimensional (1D) site response analyses to evaluate site response at ground-motion stations within the two cities, and compare the results with the current NGA-East linear amplification model and an alternate linear amplification model based on geospatial predictor variables. The improved performance of the alternate geospatial-based ergodic linear amplification model in Memphis indicates that the geospatial predictor variables of sediment thickness and adjusted physiographic province are useful for estimating site amplifications in regions with deep sediments in the CEUS. All linear site amplification models have challenges at shallow sediment sites, highlighting the difficulty in modeling site response at shallow sediment sites with strong impedance contrasts and the need for higher-resolution sediment thickness data in the entire CEUS. This study also highlights the limitations of ergodic ground-motion modeling and the benefits of site-specific or city-scale ground response analysis within vulnerable cities, especially in capturing changing behavior at a smaller spatial scale.