GEOPHYSICAL AND NEOTECTONIC EVIDENCE OF QUATERNARY REVERSE FAULTING IN THE NORTHERN WIND RIVER BASIN, WYOMING

The Stagner Creek Fault, near the southern margin of the Owl Creek Mountains, is one of a several of WNW-ESE striking faults in central Wyoming that demonstrate quaternary activity. Owing to low slip rates, surface expressions such as fault scarps can have subtle landscape expressions. This study assesses the neotectonic geomorphology and near-surface fault geometry of the Birdseye Creek section of the Stagner Creek Fault system. Microgeomorphology was analyzed using a high resolution surface model produced from low-altitude aerial photogrammetry. More than 1700 aerial photographs were collected using small unmanned aerial vehicles (sUAVs) along a ~2 km swath along the fault. The resulting point cloud has a density of ~400 points per square meter. False sun-shading of a 10 cm digital elevation model allows reliable mapping of the fault scarp despite its low relief of 30 cm. A significant result is identification of fault scarp within the Holocene surface – a previously undocumented result that changes the estimate of timing for the last surface-rupturing event. In order to constrain fault geometry, two shallow seismic reflection profiles were obtained using a rolling-spread technique with geophone spacing of 2 meters, and shot spacing of 6 meters. A fixed-spread seismic refraction line was also obtained for use in creation of a seismic velocity model for the area. This velocity model showed a simple two-layer structure representing ~10 meters of alluvium on top of Wind River Formation bedrock. Shallow seismic reflection profiling suggests the controlling fault is a north-dipping reverse fault. Due to the high-angle nature of this reverse faulting, its proximity to the adjacent Owl Creek Mountains, and the tectonic setting of the Wind River Basin, we believe this faulting may represent Quaternary reactivation of a Laramide-age reverse fault.