Abstract

A three-dimensional (3-D) shear-wave velocity (Vcontent>S) model was developed for the heterogeneous sediments of the Las Vegas Valley (LVV) in Nevada. The model was based on more than 200 Vcontent>S profiles (one-dimensional representation of Vcontent>S versus depth) and 1,400 geologic well logs. Incorporation of the well logs into the model was accomplished by condensing the geologic-log descriptions of the shallow sediments into five sediment units and then correlating Vcontent>S to these units. Characteristic Vcontent>S profiles were defined to represent four of these units by correlating between closely spaced pairs of Vcontent>S measurement sites and wells located within 500 m. These characteristic profiles were then used to generate Vcontent>S profiles at each well location by assigning Vcontent>S based on logged sediment type with respect to depth. The fifth unit was cemented sediment, for which a constant, depth-independent Vcontent>S value was assigned. Using the software EarthVision, the Vcontent>S profiles were interpolated in three dimensions, considering faults, to nearly 400 m in depth. Using regional data from an existing gravity-based survey, the model was extended to Paleozoic bedrock, which is locally deeper than 4 km. A 3-D section of the model demonstrated strong variability of Vcontent>S both laterally and vertically. Model accuracy varied spatially with data density. This model can be used to forecast earthquake ground-shaking patterns throughout the LVV. Particular application in engineering seismology can be found for high-rise structures that are vulnerable to long-period ground motion in a deep sedimentary basin.

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