Subsurface Characterization of the Quaternary Active Cheraw Fault in Southeastern Colorado Based on Seismic Imaging

Abstract

The subsurface structure of the late Quaternary active Cheraw fault is relatively unstudied. Vertical displacement estimates of faulted bedrock horizons, characteristics of bedrock structure (e.g., dip), potential association with dissolution of underlying Permian evaporite strata, and whether or not a postulated northeast extension of the topographic scarp is associated with Quaternary faulting have remained open questions. In this study, we assess six 2D seismic reflection profiles that cross the Cheraw fault scarp, demonstrate how Quaternary normal faulting has reactivated pre-existing structures along the northwest flank of the Las Animas arch, and provide new constraints for seismic hazard characterization. We map the fault to depths of at least 1.5–1.8 km into lower Paleozoic strata in which the continuity of the fault through Permian evaporite indicates that dissolution of those stratigraphic intervals has no role in Quaternary surface faulting. Interpretation of the seismic data reveals an ∼75°±5° northwest-dipping fault with ∼24–30 m vertical displacement of upper Cretaceous strata, which coincides with Quaternary scarps at the surface.