SURFACE FAULTING AND POSSIBLE KINEMATICS OF THE EAST TENNESSEE SEISMIC ZONE

The East Tennessee seismic zone (ETSZ) trends NE-SW through the Appalachians from SE KY through East Tennessee into NE Georgia and NE Alabama. It is the second most active zone in the eastern U.S. after the New Madrid seismic zone (NMSZ). Previous fieldwork recently identified the first known ETSZ surface coseismic faulting in a Pleistocene alluvial terrace along the French Broad River: a 055^o/SE-dipping fault that thrusts Ordovician shale (containing 035^o/vertical fissures filled with 15 ka alluvium) 1 m NW over French Broad River terrace alluvium.

Our new fieldwork identified surface faulting in an alluvial terrace along the Little Tennessee River near Vonore, TN: a NE-striking/SE-dipping normal fault with >2 m throw. Pleistocene alluvium is faulted against Cambrian Nolichucky Shale and drag folded into a SE-dipping structural terrace near the fault. A prominent NW-striking set of sub-vertical joints occurs in the alluvium. An OSL age of ~17 ka was obtained from the alluvium, but previous terrace mapping suggests it may be a higher, older terrace.

Faulting at Vonore is within the zone of highest concentration of ETSZ epicenters that trends 060^o and projects to the thrust faulting along the French Broad River. These young faults and earthquakes may define a principal corridor of ETSZ tectonism with characteristics similar to the NMSZ. For example, the Reelfoot thrust and the Crittenden County fault in the NMSZ are contractional faults that caused parallel bending-moment extensional faulting and fracturing at shallow depths, like the French Broad River fissuring and Vonore faulting. This NE-trending corridor of ETSZ tectonism (>130 km long) may be part of a NE-trending, SE-dipping strike-slip system with thrust and normal fault stepovers that is compatible with the modern stress field and first-motion studies of the ETSZ.