Paleoseismological studies in the Charleston, South Carolina Region

Abstract

The project was aimed at digging long, shallow trenches across anticipated near surface manifestations of earthquake prone faults in the Charleston region with the anticipation of studying them. Before the trench locations are decided, geophysical surveys were carried out to determine the optimum locations for digging. In the Colonial Fort Dorchester State Park in Summerville, S.C. a shallow trench was dug across a line joining the crack which displaced the north and south walls of a historic fort. In this trench a prehistoric seismically induced sand blow was discovered attesting to the occurrence of prehistoric earthquakes on this fault. In Magnolia Plantation, a family tomb was cracked during the 1886 Charleston earthquake. The crack on opposite side of the tomb walls suggested that the associated Ashley River fault trended NW-SE. This fault was detected on two suitable located resistivity profiles, suggesting that ARF is oriented N55°W-S55°E along the Ashley River between Magnolia Plantation and Middleton Place. The exercise also revealed that it may be possible to detect the location of seismogenic faults by shallow geophysical techniques.