89-12 Geophysical Investigations of Quaternary Faulting Along the South Granite Mountains, Wyoming

Session: Advancing Earthquake Geology and Surficial Deformation from Geologic Provinces to Political Entities through Multidisciplinary High-Resolution Data

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This study combines multiple geophysical methods to investigate the structural nature of Quaternary deformation in the South Granite Mountains of Wyoming.  In particular, a combination of electrical resistivity and seismic imaging provide constraints on fault geometry and Late Cenozoic fault displacement.  The South Granite Mountains Fault Zone, located adjacent to the Wind River Basin, is one of several Cenozoic faults in the region that exhibits evidence of continued Quaternary deformation.  The South Granite Mountains uplifted during the Late Cretaceous Laramide orogeny (75-45 Ma), and subsequently experienced Miocene extension in the formation of the Sweetwater Graben.  Recent (Late Quaternary) deformation expressed as fault scarps along the north side of the Granite Mountains.  This study focuses on faulting in the vicinity of Cherry Creek, an area previously studied in the 1980s. Seismic reflection and refraction surveys involved a ~220m long, fixed-spread geometry using a 2-meter geophone spacing.  Electrical resistivity imaging was acquired using a 200-meter rolling-spread geometry to acquire a total profile of 400 meters length and 5-meter electrode spacing.  Seismic reflection data document the northward dip of Late Quaternary faults, which suggests that Late Quaternary faulting may involve reactivation of extensional Miocene structures, rather than Laramide reverse faults.  Furthermore, joint analysis of seismic refraction and electrical resistivity tomography suggests 10 – 15 meters of throw of the Miocene-age Split Rock formation.  These subsurface investigations are combined with high-resolution, microtopograhic analysis collected using low-altitude aerial surveying (i.e., drones).  Combining the imaged fault geometry with scarp-degradation modeling of these topographic data suggest Late Quaternary slip rates of 0.03 – 0.05 mm/yr.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11364

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