Geophysical and Geological Evidence for Quaternary Displacement on the Caborn Fault, Wabash Valley Fault System, Southwestern Indiana

The Late-Precambrian-Early-Cambrian WabashValley fault system (WVFS) in the central United States is located in an area with a recognized historic and contemporary record of small-to-moderate sized earthquakes. Moreover, the prehistoric record indicates paleoliquefaction evidence for larger earthquakes with magnitude estimates ranging between M 6.2 and 7.3. However, the relationship between the seismicity and theWVFS remains poorly understood. We completed an integrated geophysical and geological drill core sampling survey across one of theWVFS's primary structures, the Caborn fault, for Quaternary displacement. The results show two high-angle fault strands deforming and displacing near-surface Quaternary sediment. The contact between the bedrock and overlying Quaternary sediment displayed nearly 10 m of vertical displacement attenuating to 1.1 m across an ostracode marker horizon approximately 4 m below ground surface. Deformation within Quaternary sediment broadens in the near surface and displays asymmetric antiformal folds that are likely indicative of a transpressional reactivation mechanism. Carbon-14 dating of the displaced sediments constrained the reactivated faulting between approximately 20 and 0.5 ka B.P. Collectively, these data provide additional first-order seismic hazard spatial and temporal parameters to the largely unknown neotectonic history of an area with uncertain seismic hazard.