A New Method for Locating Possible Active Faults Beneath the Lower Coastal Atlantic Plain, Southeastern USA

Localized uplifts, generated by active subsurface faults, affect (1) Pleistocene shoreline-regression and (2) shoreline-perpendicular rivers that advanced seaward during regression. Patterns of shoreline and river deflections help define locations, approximate orientations (shoreline-parallel or -perpendicular), lengths, and relative sense of displacement of possible active faults even in seismically quiescent areas. Models patterns are compared with patterns near the 1886 Charleston, SC earthquake and other anomalous areas. Models have maximum displacement at the center of the fault and sufficient uplift to affect surface processes. Models are: (1) regional shoreline regression without localized uplifts; (2) regression with a shoreline-parallel fault with (A) seaward-side up and (B) seaward-side down; and (3) regression with a shoreline-perpendicular fault. Model 1: consistently spaced, parallel shorelines; and an absence of river deflections. Model 1 characterizes most of the Lower Coastal Plain across Georgia. Model 2A: interruption of Model 1 patterns with convex-seaward deflection and wider spacing of older shorelines across uplift; river deflections toward uplift-margins. Model 2B: convex-landward deflection and wider spacing of younger shorelines on the downdropped side of fault; river deflections toward uplift-margins. Model 3: convex-seaward deflection and wider spacing of older shorelines across the uplift with river deflections toward uplift-margins; convex-landward deflection and wider spacing of younger shorelines on the downdropped side of fault where rivers deflect toward the lowest area; shorelines are discontinuous and difficult to correlate across the fault. Fault lengths are constrained by seaward-resumption of Model 1 shorelines. Model 3 patterns occur near the 1886 Charleston earthquake indicating a NW-trending, about 50km long, NE-side up fault. Similar patterns across the Pee Dee River suggest a comparable fault may be present there