TRANSVERSE TOPOGRAPHIC DRAINAGE BASIN ASYMMETRY ANALYSIS TO EVALUATE FAULTING IN SOUTH CAROLINA

Strong earthquakes have rocked South Carolina in the past, the largest was in 1886 measuring an estimated 6.6 – 6.9 in magnitude, causing liquefaction in Charleston. Despite several neotectonic studies of this area, seismogenic faults remain elusive. The goal of this study was to apply transverse basin asymmetry analysis to the coastal plain of South Carolina to map fault blocks and associated ground warping.

Following this analytical method, a transverse basin asymmetry vector denotes the direction and degree to which a river deviates from the basin midline. Regional basin asymmetry is expressed as a vector map, where raw vectors are spatially averaged and the resultant mean vector field is plotted within the study area. Domains of similar mean vectors are delineated to show areas of preferred basin asymmetry. ARC_TM software was used in the processing of USGS NED files and defining of river segments and basin divides. SpheriStat_TM was used to spatially average and statistically analyze the data set and provide a digital map of the vectors, after which Canvas_TM was used to assign each vector the proper magnitude and display the finished vector field for interpretation. These results were compared to seismic maps of the area, local geology, previously mapped faults, and USGS topographic maps.

Several geomorphic domains showing high levels of mean vector uniformity were identified. Pleistocene, Pliocene and Miocene unconsolidated sediments crop out in the study area, mitigating stratigraphic controls on river migration. Thus, these domains suggest crustal tilting and ground warping. These domains did not trend down structural dip of resistant units, and they are robust with respect to the parameters of the spatial averaging program. A zone of randomly oriented mean vectors trending NW-SE divides the prominent domains into two clusters, and this zone corresponds to the principle seismicity trend. No surface faults are mapped here, however this trend is collinear with the Blake Spur transform as mapped offshore. Documented faults control the margins of some domains, for example the Garner-Edison fault and Gants fault