Abstract

Geomorphic, geologic, and geophysical data suggest the presence of an ~600-km-long, north-northeast-trending buried fault system in the Coastal Plain of the Carolinas and Virginia, herein named the East Coast fault system. The East Coast fault system is expressed by anomalous changes in alluvial geomorphology that locally concide with one or more of the following features: linear aeromagnetic anomalies, buried faults intepreted from seismic reflection data, surface faults offsetting Pliocenc-Pleistocene surficial units, locally brecciated phyllites and argillites, gently upwarped sediments, topographic highs, and seismicity near Summerville, South Carolina.

River anomalies where the rivers traverse unconslidated upper Pleistocene-Holocene flood-plain sediments are evidence of deformation along the East Coast fault system during the past 130 to 10 k.y. which may be ongoing. The fault system traverses the epicentral area of the 1886 Charleston, South Carolina, earthquake and lies west of paleoliquefaction sites along the outer South Carolina Coastal Plain; thus, the fault system could be the source of the Charleston earthquake and other large prehistoric earthquakes. Therefore, confirmation and determination of the East Coast fault system and elucidation of its history will help better assess seismic hazards in the southeastern United States.