Finding Faults in the Charleston Area, South Carolina: 2. Complementary Data

摘要

The seismotectonic framework associated with the MiddletonPlace-Summerville seismic zone (MPSSZ) inferred from seismicity data consists of the similar to 50-km-long, similar to N30 degrees E-striking, NW-dipping, Woodstock fault associated with right-lateral oblique strike-slip motion, with a similar to 6-km-long antidilatational left step near Middleton Place, dividing it into the Woodstock north and south faults. Three similar to NW-SE striking reverse faults, two NE dipping and one SW dipping, were recognized within this step. The Woodstock (N) fault lies along the southeast boundary of a buried Triassic basin, and the current seismicity is due to its reactivation. A comparison of this seismotectonic framework using a Geographic Information System shows that it is consistent with available geomorphological, geodetic, shallow stratigraphic (<150 m), seismic reflection and refraction, and potential field data, some of which were used in Dura-Gomez and Talwani (2009) to develop it. It further suggests that ongoing tectonic activity on the faults comprising this framework has resulted in breaking the overlying basalt along the Woodstock fault and in warping of the overlying sediments. Continuous vertical movements along the NW-SE stepover faults has resulted in uplift on the NE and SW bounding faults with the formation of the Mount Holly and Fort Bull domes. We found that these interpretations of complex faulting on multiple faults in the MPSSZ agreed with and explained the observed macroscopic data gathered after the 1886 Charleston earthquake.