STRUCTURAL DEFORMATION OF THE ROUGH CREEK GRABEN WITHIN THE STABLE CRATON OF CENTRAL NORTH AMERICA

The Rough Creek Graben (RCG) is one of the prominent structural warps in Kentucky situated within the stable craton of central North America. It has been an important area of interest due to its proximity to the current ‘seismic hot spots’, the New Madrid Seismic Zone (NMSZ) of the Reelfoot Rift in the south and the Wabash Valley Seismic Zone (WVSZ) in the north. Much of the kinematics, slip variation, and evolution of the RCG structures are poorly constrained that limits a complete understanding of fault dynamics in relation to seismic behavior in the region. While previous studies have mapped faults in seismically inactive RCG through a combined effort of field and geophysical techniques, a detailed mapping of the area is hindered by the paucity of outcrops and thick accumulations (up to 100s of meters thick) of overlying Quaternary strata.

Here, we investigate the graben-forming faults through an integrated approach of (1) SRTM and ASTER DEMs derived geomorphic signals, drainage deflection patterns, comparisons of hillshades with variable illuminations, and shadow-illumination effects and (2) field-based structural synthesis to obtain a 3D structural model of spatial distribution and geometry of faults, and seismic energy propagation feedback throughout the system. Our results demonstrate presence of mostly NE-SW trending normal faults with high angle slips, distinct horizontal and vertical displacements and fault damage zones. Majority of these faults are oppositely dipping and likely transfer faults that result from extensional stresses associated with the RCG. Presence of less frequent reverse and thrust faults, folds, and smearing suggest that these compressional structures are likely the result of strain localization within the graben. We interpret that the structures of RCG might develop in a brittle-ductile shear zone associated with the stress regime and growth of RCG.

Understanding the deformation histories of the studied graben are crucial for delineating the structural behavior of the faults and synthesizing it's stress field reactivation to modern seismicity in response to an earthquake originating from either the NMSZ or WVSZ. Our findings will not only better assess earthquake hazards but also advance our knowledge of the complex evolution of continental rift dynamics.