PALEOSEISMIC INVESTIGATIONS IN THE EAST TENNESSEE SEISMIC ZONE

The East Tennessee seismic zone (ETSZ) is an elliptically shaped intraplate seismic zone that extends from NE Alabama and NW Georgia into SE Kentucky. The ETSZ occurs in the southern Appalachian Valley and Ridge where the bedrock consists of Cambrian to Pennsylvanian siliciclastic and carbonate rocks that were deformed into a foreland fold-thrust belt during the late Paleozoic Alleghanian orogeny (325-260 Ma). Seismicity is located at 7-25 km depths in the basement beneath the foreland fold-thrust belt, and the current orientation of S_Hmax is 070 in the eastern United States. Despite having a high rate of seismicity in the eastern U.S., limited detailed investigations of the paleoseismic history of the ETSZ have been conducted until now.

Our recent work has identified two Quaternary faults (1 normal, 1 thrust) exposed near Vonore, TN ~48 km SW of Knoxville, TN, a thrust near Dandridge, TN, ~45 km E of Knoxville, and another thrust near Maryville, TN, ~15 km S of Knoxville. The faults at all three localities have NE-striking, SE-dipping orientations, cut late Paleozoic structures, contain characteristic red, sandy clay-filled fault gouge, and fault Cambrian and Ordovician shale against Quaternary river deposits. All of the faults identified to date align along a N60E deformation zone, and have 1-2 m of displacement, suggesting these faults are related to a large fault at depth produced by M > 6 earthquakes.

Google Earth^TM maps were used in SE Tennessee to investigate if paleoseismic features are restricted to the N60E corridor, or if additional narrow zones occur within the seismic zone. This reconnaissance yielded several widely distributed localities containing red sandy-clay filled fractures, but only one near Tellico Plains, TN, ~24 km SW of Vonore, TN, contains abundant red clay-filled faults of unknown displacement up to 5 cm-thick. These faults trend NE and NW (conjugates?) and exhibit down-dip oriented slickensides (hanging wall both up and down) and cut a deeply weathered debris-flow containing matrix-supported chert clasts and a few sandstone boulders. Chert clasts are displaced ~3 cm by a thrust. Faulting here is consistent with previously identified localities that indicate NW-SE shortening, and suggests a difference between the current stress field and the stress field during faulting.