The locations and morphologies of Mesozoic half-grabens in the southeastern United States Piedmont are generally believed to have been controlled by reactivation along older Paleozoic ductile-deformation fault systems. We suggested earlier (Costain et al., 1987a; Coruh et al., 1988a) that the localization may have been controlled in part by the development of a strike-slip duplex (SSD) that extends from the Brevard-Bowens Creek fault zone, its "floor" on the northwest, to near its "roof" at the eastern Piedmont fault system beneath the Atlantic coastal plain ( 300 km), and from central Virginia southwest to the Pine Mountain belt and the Towaliga and Goat Rock faults ( 1,000 km). Included in the SSD is the entire metamorphic core of the southern Appalachians except for the Blue Ridge. Seismic data from central Virginia as well as reprocessed COCORP data from Georgia reveal antiformal and synformal shapes of regional extent that may have formed by reactivation of the same Paleozoic mylonite zones during Mesozoic crustal extension. Excellent onshore seismic-reflection data have been recovered from the Culpeper, Virginia basin, the buried Jedburg basin near Summerville, South Carolina, and the South Georgia basin in Johnson and Laurens counties, Georgia. Data from the buried Jedburg basin indicated that processing single-sweep data instead of stacking source arrays results in better lateral resolution than conventional process ng methods.