NEOTECTONICS RECORDS IN THE GREEN RIVER BASIN: A NEW MORPHO-TECTONIC ANALYSIS OF TRANSIENT CHANNELS DRAINING ACROSS THE ROUGH CREEK GRABEN, WESTERN KENTUCKY

The Green River Basin, located within the Rough Creek Graben (RCG), is the largest watershed in Kentucky that includes more than 100 tributaries. These tributaries drain across two rift border faults, the Rough Creek Fault system in the north and the Pennyrile Fault system in the south of the RCG. At present, the RCG has gained significant attention for its close proximity to two seismic hot spots – the New Madrid Seismic Zone of the Reelfoot Rift in the west and the Wabash Valley Seismic Zone in the north. While previous studies have mapped the border faults of the RCG, a detailed understanding of these faults’ response to neotectonics is hindered by the paucity of fault exposures and the presence of ~8 km-thick sedimentary cover.

We used morpho-tectonic analysis of geomorphic proxies extracted from 30-meter resolution ASTER Digital Elevation Model (DEM) data and GIS-based vector data of the tributaries. We extracted a total of 311 tributary profiles from nine watersheds using stream power-law functions equipped in MATLAB and GIS. The normalized steepness index (k_sn) value ranges from 0.07 to 25.16, which varies from east to west, with the higher values in the east of the RCG. This high steepness pattern reveals transient response of the tributaries to the tectonic activity likely related to the RCG and the uplifted Cincinnati Arch. The high concavity values (0.79-13.0) are found within the north and south of the Pennyrile fault system. About 300 knickpoints are identified based on the channel steepness and concavity patterns within the tributary profiles. While the highest number of knickpoints are centralized within the graben bounded by the major rift border faults as deduced from knickpoint density calculation, a large number of knickpoints, unassociated with localized variations in lithology, likely formed due to the overall neotectonic activity in the area. This study not only helps to constrain the geomorphic proxies in investigating the tectonic-activity in the study area that is high in the central and eastern part of the Green River Basin, but also improves our general understanding of river response to neotectonics associated with potential seismic and landslide hazards.