DISTRIBUTION OF QUATERNARY FRACTURES AND FOLDS IN THE EAST TENNESSEE SEISMIC ZONE

The East Tennessee seismic zone (ETSZ) is the second most active area of earthquakes in the Eastern United States. Unlike the New Madrid seismic zone, a chronology and spatial distribution of paleoearthquake activities have not been developed for the ETSZ. Our team has surveyed alluvium and saprolite exposed in lake shores on the French Broad River and Little Tennessee River and in quarries in the area of greatest ETSZ activity, and has identified evidences for Quaternary paleoearthquakes. Along with fresh quarry exposures, wave actions along lake shores create well-exposed alluvium terraces for identifying fractures and other recent deformations. Early work, done by our team in 2011 and 2012, identified an area of NE-striking thrust faulting in Quaternary alluvium as well as paleoliquefaction and abundant fractures along the French Broad River. Our subsequent fieldworks discovered NE-striking faults on the Little Tennessee River, which are collinear with French Broad River thrusts. Thus, we speculate that these structures occurred in a 060º corridor of deformation, which could represent deep-seated fault zone. Red-clay filled fractures are abundant near these Quaternary faults, and we interpreted similar fractures in saprolite as Quaternary deformation.

We surveyed areas within and well beyond the 060º fault corridor to assess the possible evidence of paleoseismicity distribution in ETSZ. Preliminary evaluation of our fracture data suggests that many may be mode-I opening joints and conjugate shears related to the modern stress field. Fractures that we observed in terrace alluvium have a non-random geographic distribution, and we found them primarily in proximity to the 060º corridor defined by faults. Fractures in terrace alluvium and in saprolite are found clustered in narrow zones, and most exposures of alluvium or saprolite that are away from the 060º corridor have no fractures. Therefore, these data collectively suggest that it might be possible to construct a chronology and spatial distribution of paleoearthquake activities of ETSZ.