Discovery of a Sand Blow and Associated Fault in the Epicentral Area of the 1886 Charleston Earthquake

Abstract

An earthquake-induced sand blow was discovered in a shallow trench dug on the premises of the Colonial Dorchester State Historical Site in Summerville, South Carolina. A comparison of its location with available seismicity, seismic reflection, and shallow geological and geomorphologic data suggests that the sand blow was associated with a splay of the currently active Sawmill Branch fault zone. This is the first sand blow to be directly associated with a specific fault in the Middleton Place–Summerville seismic zone, the source zone for the Charleston earthquakes. Geotechnical and vibracore data revealed that the source sand is ∼3 m thick and the top of the sand is at a depth of ∼2.5 m below the ground surface. The sand blow was associated with a pre-1886 earthquake that occurred possibly 3,500 YBP or earlier, with an estimated maximum magnitude of 5.6.