The shallow bedrock and variable overburden across Casper Wyoming demand a subsurface investigation method capable of resolving sharp velocity contrasts without the ambiguity that often plagues conventional geotechnical drilling. Winter freeze-thaw cycles along the North Platte River corridor create fractured sandstone lenses that standard SPT drilling can easily miss, while the transition from floodplain alluvium to the Casper Formation sandstone occurs over just a few hundred feet laterally. Seismic tomography, combining refraction and reflection acquisition geometries, maps these transitions by inverting first-arrival traveltimes and stacked reflection events into a continuous P-wave or S-wave velocity model. The technique works particularly well where the water table sits within 15 to 30 feet of grade, a condition common in Natrona County, because saturated sediments produce a diagnostic velocity increase that delineates the groundwater surface without requiring a single borehole. When bedrock rippability or fault avoidance governs foundation design, the velocity cross-section from seismic tomography becomes the primary deliverable that structural and geotechnical engineers rely on, often supplemented by targeted SPT drilling at anomaly locations identified in the processed profile.
A seismic velocity cross-section resolves the transition from weathered to competent sandstone with greater lateral continuity than any feasible grid of boreholes.
