POSSIBLE CONTRIBUTION TO SOUTHERN BLUE RIDGE RELIEF FROM QUATERNARY FAULTING IN THE EASTERN TENNESSEE SEISMIC ZONE

In the Appalachians Mountains, the great majority of summits above 1800 m are found in the southern Blue Ridge of Tennessee and North Carolina. A growing body of evidence that supports late Cenozoic rejuvenation of the southern Appalachian region includes crustal cooling rates, abnormal crustal thicknesses, increased sediment delivery to depocenters, and high elevation relict fluvial and lacustrine sediments. This and evidence from a fossil vertebrate site in NE TN suggest recent uplift began in late Miocene/early Pliocene. Consistent with recent uplift, our field investigations reveal Quaternary faults 5 to 20 km W of the western Blue Ridge escarpment and aligned in a 060^o corridor within the eastern Tennessee seismic zone (ETSZ). This 80 km-long corridor—the Dandridge-Vonore fault zone (DVFZ)—contains a series of northeast-striking faults having 1-2 m up-on-the-southeast displacements exposed on the French Broad River (Dandridge site), the Little River (Alcoa site), and the Little Tennessee River (Vonore site). The DVFZ partially overlaps a trend of seismicity that extends at least 30 km farther SW, indicating a total length of >110 km.

The DVFZ and highest ETSZ earthquake density are both within the zone where recently published modeling predicts a maximum unclamping of faults would occur due to erosional unloading of the mountains. Thus, the DVFZ may be a principal structure accommodating recent isostatic uplift of the southern Appalachian Blue Ridge. Convexity in Little Tennessee River terraces at Vonore, TN, shows increasing amplitude with increasing terrace age, suggesting an average uplift rate across the DVFZ (SE side up) of 0.05 mm/yr (50 m/m.y). This rate is greater than the 6 to 20 m/m.y. erosion rate estimated from in situ cosmogenic ¹⁰Be data for summits in the Appalachians, suggesting slip rate on the DVFZ is adequate to give rise to the elevation of the Blue Ridge summits over the long term.