QUATERNARY FAULTING IN UNION COUNTY, KENTUCKY: PRELIMINARY RESULTS

Geomorphic field evidence and high-resolution SH-wave seismic reflection profiles suggest that a scarp, located within the active floodplain of the Ohio River in Union County, Kentucky, is a fault scarp associated with the Hovey Lake Fault, a part of the Wabash Valley Fault System. The scarp trends due north along a straight line for nearly 5 km and terminates as it approaches the Ohio River. At the southern end of the scarp, the eastern side is 2.5 meters higher than the downthrown western side, but to the north this elevation difference becomes progressively less apparent because of overbank floodplain sedimentation.

Several geomorphic indicators suggest this is a fault scarp and not an erosional terrace cut by the Ohio River. Many drainage channels on the eastern side of the scarp flow to the west and can be followed on the downthrown side of the scarp, implying that the two surfaces were once at the same elevation. Geomorphic mapping indicates that in the past, the Ohio River flowed south-southwest for a relatively long period, then abruptly changed direction and locally flowed northwest. Furthermore, immediately north of the scarp the Ohio River has three straight sections that are separated by 90-degree turns, creating three sides of a box that flows around the scarp. This geomorphology suggests that the course of a south-flowing Ohio River was perturbed by surface faulting, and the river adjusted its course by flowing north around the deformation, similar to events that occurred at the Reelfoot Fault on the Mississippi River in 1812.

Three high-resolution SH-wave seismic reflection profiles, two across the southern projection of the scarp and one north of the scarp on the southern bank of the Ohio River, show displaced Quaternary strata to within 5 m of the ground surface, supporting our interpretation that the scarp is indeed a fault scarp.