NEOTECTONIC ACTIVITY IN THE CHARLESTON, SOUTH CAROLINA REGION

We examined detailed gravity(1mGal CI), magnetic(20nT CI) and shallow Tertiary stratigraphic data (inferred from biostratigraphic correlation of data from over 1000 auger and 9 core holes) in the meizoseismal region of the 1886 Charleston S.C. earthquake. These data were examined with available seismicity, Minisosie, shallow seismic reflection and geomorphology data to understand the seismogenesis in the region. The shallow stratigraphic data show the absence of layered cake stratigraphy,and instead show evidence of six shallow domes surrounded by subsurface troughs, attesting to complex interaction among deposition, erosion and tectonic warping through time. Comparison of these features with short wavelength anomalies in the potential field data reveal that some shallow subsurface features lie atop deeper structures associated with gravity highs, suggesting a causal and spatial relationship. Other domes in the stratigraphic record do not show a correlation with the potential field highs, but instead appear to be the result of tectonic uplift resulting from neotectonic activity on buried faults. Evidence of tectonically related uplift was found on the NNE trending Woodstock fault (zone of river anomalies, warped shallow sediments) and on the Ashley River fault (uplift near Summerville). These uplifts lacking corroborative gravity highs are interpreted to be the result of tectonic activity on buried faults since the Eocene. Understanding the complex interaction of these buried structures in the presence of present day tectonic stress field explains the current seismicity and the seismic potential of the region.