FIELD EVIDENCE OF LATE QUATERNARY FAULTING IN THE EASTERN TENNESSEE SEISMIC ZONE NEAR KNOXVILLE AND IMPLICATIONS FOR SEISMIC HAZARD

The Eastern Tennessee seismic zone (ETSZ) exhibits one of the highest rates of seismicity in North America east of the Cordillera. Instrumentally located earthquakes reveal the ETSZ trends N45E from northern Alabama and northwestern Georgia to southeastern Kentucky and western Virginia. In the area of greatest seismicity near Vonore, TN, a secondary N60E alignment of earthquakes (and topographic lineament) crosses the principal seismicity trend. The longitudinal profile of a late Pleistocene/early Holocene terrace along the Little Tennessee River is convex with an amplitude of 1 m at Vonore, and discontinuous older terraces suggest larger convexities at Vonore. NE-striking late Quaternary faults at Vonore, Maryville, TN, and Dandridge, TN, occur in a corridor extending 80 km northeastward and are collinear with the N60E seismicity alignment. Thrust, normal, and strike-slip faults have been observed, but prominent SE-up thrust faults are present at each locality. Optically stimulated luminescence dating of faulted and post-faulting sediments delimit faulting events to <17 ka at Vonore, to <13 ka and from 13 to 16 ka at Maryville, and to <13 ka and to 13 to 17 ka at Dandridge.

Based on collinear strikes, SE-up sense of movement, and overlapping timing constraints of faults at all three localities, we suggest there may be a >80 km-long NE-striking master fault at depth related to these surface ruptures. Timing constraints on faulting events permit an interpretation that one or more earthquakes after 16 ka may have ruptured 80 km from Dandridge to Vonore. Such a rupture length would produce a M7+ earthquake. As presently defined, the N60E Quaternary faulting corridor crosses the ETSZ for 30 km at the point of greatest seismicity from Vonore to Maryville, but it extends 50 km northeastward of the ETSZ proper to Dandridge, where there is much less seismicity, suggesting that the ETSZ as defined by recorded earthquakes does not completely define the region of potentially seismogenic structures. In light of recent arguments for rejuvenation of the Appalachian Mountains, it is noteworthy that this corridor of SE-up Quaternary faulting lies along the transition from the western Blue Ridge 50-km crust to the atypically low-relief thinner crust of the southern Tennessee Valley and Ridge.