Geophysical features of major structural and lithostratigraphic elements in the southeastern United States: An overview

In the Alleghany Plateau and Valley and Ridge provinces, the quality of shallow and deep vibroseis reflection seismic data acquired where carbonate rocks do not crop out at the surface is generally excellent for depths up to 10 km. One interpretation of heat flow data from granitoids that are exposed east of the central Piedmont is that heat-producing crust is tectonically truncated at a depth of ca. 8 km. Seismic data over the Blue Ridge (BR) and Inner Piedmont (IP) from northwestern SC to central VA image the upward ramping (to the northwest) of the BR master decollement over a distance of at least 600 km. Strikingly similar seismic signatures near this ramp are interpreted to be from thrust nappes composed of an Early Paleozoic( ) volcanic( ) protolith. Similar signatures but from an apparently less deformed protolith have been obtained from the IP in SC. New reprocessing and interpretation of a regional seismic line in VA indicate that the easternmost extent of Paleozoic shelf strata is not far east of the surface exposure of the BR-IP boundary. Large antiforms have been imaged in central VA, COCORP Lines 5 (Kiokee antiform), and Line 8 (beneath the Coastal Plain). Eastward-dipping reflectionsmore » have been recorded beneath the Atlantic Coastal Plain from VA to GA. Reflections from Coastal Plain sediments are generally excellent. Faulted sediments of Cretaceous and younger age have been clearly imaged on reflection data in VA and SC. In some cases, these faults are upward continuations of fault-bounded Mesozoic rift basins. In the James River seismic zone, there is a good correlation between hypocenters and the roof of the antiform and structures above that are imaged in seismic reflection sections. In other areas of the southeastern US, the seismicity is more diffuse; however, it suggests that the Hydroseismicity hypothesis might be a viable trigger mechanism for intraplate earthquakes.« less