Re-evaluating Intraplate Seismic Hazard in the South Carolina Coastal Plain

Abstract:

Charleston, South Carolina experienced the largest earthquake recorded in the eastern United States (~7 Mw) in 1886 and continues to experience low magnitude seismic activity today. Current seismic hazard assessments risk the Charleston area significantly higher than the rest of the South Carolina Coastal Plain. However, reexamination of legacy seismic reflection data in South Carolina suggests that other basement faults may have experienced large magnitude Cenozoic seismicity. At least three locations in the South Carolina Coastal Plain show tens of meters of Cenozoic sediment deformation over basement faults. In addition, Cenozoic and Cretaceous sediments overlying active faults near Charleston have between 10 to 100 m of deformation, implying that seismic activity activity along these faults is either geologically recent or episodic. This analysis of Cenozoic fault displacement suggests that seismic hazard should be elevated more generally throughout the South Carolina Coastal Plain.