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Mesoscale Extensional and Contractional Structures in the Rough Creek Graben, Midcontinent Rift, Central United States: An Integrated DEM Analysis, 3-D Structural Modeling and Field-Based Approach

Abstract

The Rough Creek Graben (RCG), a midcontinent Cambrian rift system in central United States, is situated at the junction of two seismic zones, the New Madrid Seismic Zone and the Wabash Valley Seismic Zone. However, the RCG is seismically inactive compared to these two zones. RCG is dominated by macroscale E-W trending rift border faults with a few NE-SW trending normal faults. This graben also possesses some of the world's largest karst landscapes like the Mammoth Cave. Due to the presence of thick succession of rift-related sedimentary rocks and Quaternary sediments (~8 km) above the basement rocks, the mesoscale structures in this graben remain largely underexplored. Here, we investigated detailed structural architecture of the mesoscale structures of RCG to understand intraplate deformation. We used an integrated approach of (1) SRTM and ASTER DEM-derived geomorphic signals such as drainage deflection patterns, comparisons of hillshade images with variable illumination angles, radar shadow-illumination effects, (2) field-based structural synthesis, and (3) 3-d structural models for spatial distribution and relationship using MOVE software and GIS interface. Our results demonstrate the presence of distinct fault cores, damage zones, and mostly NE-SW and NW-SE trending high-angle normal faults that are tangential to the border faults of the graben. Majority of these faults likely originated from extensional stresses associated with the development of RCG. However, the presence of less frequent contractional structures (reverse and thrust faults and folds) suggests strain localization within this graben. Although most of these faults from our study area are seismically inactive, understanding the structural deformation history of these faults is crucial for synthesizing any fault reactivation in response to a large magnitude earthquake originating from either the New Madrid Seismic Zone or Wabash Valley Seismic Zone. Our findings not only advance our knowledge of the complex structures of a midcontinent rift system but also help assess earthquake risks. In addition, positive correlations between our mapped mesoscale fault systems and the karst landscapes suggest a relationship between these faults and the ultimate morphology of conduit systems that assist in the development of these landscapes.