Assessment of paleoseismic shaking that caused a sand blow at Fort Dorchester, SC

Abstract

A sand blow from a paleo-earthquake was identified at Fort Dorchester, South Carolina in 2007. Geotechnical field investigations indicate the thickness of the source sand layer ranges from 1.2 to 3.1 m and the depth below the ground surface to the top of the layer ranges from 2.3 to 3.9 m. The layer is predominantly angular to subangular silty quartz sand with a fines content of 4 to 22% and the predominant mean grain diameter of 0.18–0.26 mm. The geotechnical data were used with paleoliquefaction evaluation methods and two independent relations to account for soil aging to estimate the minimum magnitude and peak ground acceleration of the prehistoric earthquake. Four regionally proper Ground Motion Prediction Equations were used in combination with the back-calculated peak ground accelerations to obtain proper estimation of a max -M. For a range of site-to-source distance from 4 to 10 km, the minimum earthquake magnitude and peak ground acceleration of prehistoric earthquakes at the Fort Dorchester site ranges from 5 to 6.3 and 0.19 to 0.39 g respectively.