Validation of tectonic models for an intraplate seismic zone, Charleston, South Carolina, with GPS geodetic data

Although the average strain rate in intraplate settings is 2--3 orders of magnitude lower than at plate boundaries, there are pockets of high strain rates within intraplate regions. The results of a Global Positioning System survey near the location of current seismicity (and the inferred location of the destructive 1886 Charleston, South Carolina earthquake) suggest that there is anomalous strain build-up occurring there. By reoccupying 1930 triangulation and 1980 GPS sites with six Trimble SST dual frequency receivers, a strain rate of 0.4 {times} 10{sup {minus}7} yr{sup {minus}1} was observed. At the 95% confidence level, this value is not significant; however, at a lower level of confidence ({approximately} 85%) it is about two orders of magnitude greater than the background of 10{sup {minus}9} to 10{sup {minus}10} yr{sup {minus}1}. The direction of contraction inferred from the GPS survey 66{degree} {+-} 11{degree} is in excellent agreement with the direction of the maximum horizontal stress (N 60{degree} E) in the area, suggesting that the observed strain rate is also real. 66 refs.