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Regional seismic velocity model for the U.S. Atlantic and Gulf Coastal Plains based on measured shear wave velocity, sediment thickness, and surface geology

Cassie Gann-Phillips·Ashly Cabas·Chunyang Ji·Chris H. Cramer·James Kaklamanos·Oliver S. Boyd
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Abstract

The Atlantic and Gulf Coastal Plains (CPs) are characterized by widespread accumulations of low-velocity sediments and sedimentary rock that overlay high-velocity bedrock. Geology and sediment thickness greatly influence seismic wave propagation, but current regional ground motion amplification and seismic hazard models include limited characterization of these site conditions. In this study, a new regional seismic velocity model for the CPs is created by integrating shear wave velocity (V S ) measurements, surface geology, and a sediment thickness model recently developed for the CPs. A reference rock V S of 3000 m/s has been assumed at the bottom of the sedimentary columns, which corresponds to the base of Cretaceous and Mesozoic sediments underlying the Atlantic CP and the Gulf CP, respectively. Measured V S profiles located throughout the CPs are sorted into five geologic groups of varying age, and median V S profiles are developed for each group by combining measured V S values within layer thicknesses defined by an assumed layering ratio. Statistical analyses are also conducted to test the appropriateness of the selected groups. A power law model with geology-informed coefficients is used to extend the median velocity models beyond the depths where measured data were available. The median V S profiles provide reasonable agreement with other generic models applicable for the region, but they also incorporate new information that enables more advanced characterizations of site response at regional scales and their effective incorporation into seismic hazard models and building codes. The proposed median velocity profiles can be assigned within a grid-based model of the CPs according to the spatial distribution of geologic units at the surface.

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Cassie Gann-Phillips, Ashly Cabas, Chunyang Ji, Chris H. Cramer, James Kaklamanos, Oliver S. Boyd. 2024-02-16. Regional seismic velocity model for the U.S. Atlantic and Gulf Coastal Plains based on measured shear wave velocity, sediment thickness, and surface geology. https://doi.org/10.1177/87552930231222960

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