P- And S-wave seismic modeling of the shallow subsurface across the Cheyenne belt in the Sierra Madre Mountains

We used multicomponent seismic reflection/refraction data to determine seismic velocities, Poisson's ratios and geometries of shallow subsurface structures across the Cheyenne Belt, an Archean-Proterozoic boundary in southeastern Wyoming. The travel-times of P-wave first arrivals were inverted to obtain a model of both P-wave velocity and subsurface geometry. Since S-wave data quality was inferior to that of the P-wave data and S-wave ray coverage of the subsurface was discontinuous, we proposed a method to estimate Poisson's ratio using SiO₂ concentration and the average atomic weight (AAW) of a formation with known mineral and oxide compositions. Subsequently, the final P-wave velocity model was converted into an initial S-wave model using Poisson's ratios estimated by this method. The S-wave data were inverted for velocities only, keeping the subsurface geometry derived from P-wave inversion constant. The inversion of P- and S-wave travel times resulted in a shallow subsurface model of rock properties, which was interpreted based on surface geology and Poisson's ratio variations to provide a near-surface geological structure model.