Quaternary fault reactivation in the fluorspar area fault complex of western Kentucky'. Evidence from shallow SH-wave reflection profiles

Shallow shear-wave seismic-reflection profiles were collected over the southwestern projection of the Fluorspar Area fault complex into the northern Jackson Purchase region of western Kentucky. The area lies at the northern end of the sediment- filled Mississippi embayment, where the Paleozoic carbonate rocks are masked by a relatively thin, approximately 100 m sequence of nonlithified Cretaceous, Tertiary, and Quaternary sediments. The interpreted profiles imaged clear evidence of fault and apparent fold propagation into the near-surface Quaternary units. The profiles also showed evidence of various structural styles associated with episodic movement. The exact timing of the latest tectonic episode exhibited on the profiles is not known because of the lack of more accurate stratigraphic detail coincident with the lines. However, physical evidence of Quaternary deformation less than 10 m below the ground surface, along with the instrumentally recorded seismic events located in the immediate vicinity of the study area, emphasizes the problematic nature of these fault segments for the design of critical or high-hazard structures.