Seismotectonic structures along the Savannah River Corridor, South Carolina, U.S.A.

Abstract

The Savannah River Corridor is defined herein to extend from the Brevard zone in South Carolina to just northwest of Charleston, South Carolina. The length of the Corridor is 400 km, the width 300 km, and the strike is S 40°E. The Corridor includes (1) the Savannah River Site, which is the locus of the most detailed seismic reflection data set in the eastern United States, and is the keystone for the extrapolation of regional reflection seismic data away from the Site, and (2) the South Carolina–Georgia seismic zone. The principal data used for the conclusions of this study are reflection seismic data acquired by the Consortium for Continental Reflection Profiling (COCORP), the Appalachian Ultra-Deep Core Hole (ADCOH) project, and Conoco, Inc. (SRS). Relatively higher seismicity appears to be associated with a crustal scale antiform that has been imaged in the Savannah River Corridor as well as to the northeast along strike in Virginia. An increase in earthquake activity occurs in that part of the crystalline allochthon that overlies and conceals a foreland-dipping imbricate stack that has developed in early Paleozoic rocks beneath the overthrust Piedmont crystalline allochthon. To the southeast, hypocenters of two SRS earthquakes (1985 and 1988), projected along the strike of the Pen Branch northwest-bounding fault of the Dunbarton Triassic rift basin plot on a highly reflective southeastward-dipping shear zone that underlies the basin. Here, the proximity of the hypocenters to the border fault of the Dunbarton basin suggests that syntectonic structures associated with the Pen Branch border fault might be involved. Some of the seismicity is probably associated with reactivation of older Paleozoic and Mesozoic structures.