Development of a site response and hazard model for the US Atlantic and Gulf Coastal Plains, Geo-Risk 2023: Hazards and Climate Change, 23–26 July 2023, Arlington, Va.
Document Type
Conference Proceeding
Publication Title
American Society of Civil Engineers (ASCE): Geo-Risk 2023
Publication Date
7-23-2023
Meeting Name
Geo-Risk 2023
Meeting Date
July 23–26, 2023
Meeting Location
Arlington, Virginia
Abstract/ Summary
The Atlantic and Gulf Coastal Plains (CPs) in the eastern, southeastern, and southern US consist of deep unconsolidated sediments overlying a high-velocity bedrock, which can significantly affect the amplitude and duration of earthquake ground motions in the region. Evaluating seismic hazards in the US CPs requires an in-depth understanding of how both geology and sediment thickness influence seismic wave propagation in the region. Existing site amplification and seismic hazard models for the Atlantic and Gulf CPs are limited in their characterization and modeling of these factors. Our project seeks to develop a characterization of site response in the CPs and incorporate it into probabilistic seismic hazard estimations for the region. In this paper, we describe our preliminary one-dimensional site response analysis (SRA) simulation results, which include using a new sediment thickness model, randomization of shear wave velocity (VS) profiles, and a reference velocity at the base of the soil columns of interest equal to 3,000 m/s. Our preliminary site response model is compared to other available amplification models by focusing on their implied characterization of amplification factors as a function of sediment thickness and ground shaking intensity. We find that at low frequencies (i.e., 0.5 Hz, or 2 s period) our site amplifications are in good agreement with VS30-based (the average shear-wave velocity in the top 30 m) NGA-East models for thinner sediment thicknesses, but this is not the case for larger sediment thicknesses (>100 m). Also at low frequencies, our model is in good agreement with existing amplification models in the region that directly account for sediment thickness. At higher frequencies (i.e., 10 Hz, or 0.1 s period) our preliminary model provides a similar trend to existing sediment-thickness-dependent models, but it does not show the same decrease in amplification for larger sediment thicknesses. Additional comparisons at specific locations of interest, such as Charleston, South Carolina, and Memphis, Tennessee, reveal that our model provides an upper bound of amplifications at low frequencies for younger and thicker deposits, and a lower bound at high frequencies. The latter trend may be explained by the assumed seismic attenuation quality factor (Q) properties in our model.