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Seismotectonics of the southern Appalachians

TENNESSEE EARTHQUAKE INFORMATION CENTER MEMPHIS STATE UNIVERSITY, MEMPHIS, TENNESSEE 38152

Abstract

The southern Appalachians of eastern Tennessee and western North Carolina is a region for which high quality instrumental seismic data have been very limited. In this paper, we report more than 100 new or relocated hypocenters obtained from the initial yr of operation of the Southern Appalachian Regional Seismic Network (SARSN), a 16-station, four-state telemetered network of short-period vertical instruments. These data provide a first-order snapshot of southern Appalachian seismicity that confirms some previous observations and adds new results for the region. The most important new observations are well-constrained focal depths and focal mechanisms for southern Appalachian earthquakes. The level of activity exceeds expectations and concentrates more heavily in the Valley and Ridge Province of eastern Tennessee—as opposed to the Blue Ridge or Inner Piedmont—than is evident in historical listings. The large majority of these events lie between the New York-Alabama lineament and the Clingman/Ocoee lineaments, magnetic anomalies produced by deep-seated basement structures. An analysis of the uniqueness and stability of hypocentral depth yields reliable depths for 58 earthquakes and demonstrates that most southern Appalachian seismic activity occurs beneath the decollement, thus lending quantitative support to the argument that Appalachian seismicity is unrelated to surficial geological or tectonic features. Several new focal mechanisms of a higher quality than previously available indicate that the basement of the Valley and Ridge is under NE-SW compression and the principal mode of faulting is right-lateral strike-slip on nearly north-south faults. In both depth and type of faulting, the seismogenic model we propose for the southern Appalachians closely emulates the Giles County zone to the north of our study area.

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