Tenth U.S. National Conference on Earthquake Engineering Frontiers of Earthquake Engineering July 21-25, 2014 Anchorage, Alaska 10NCEE Reassessment of Prehistoric Earthquake Accelerations at Sampit and Gapway Sites in the South Carolina Coastal Plain E. Gheibi 1 and S. L. Gassman 2 ABSTRACT Current empirical procedures to evaluate soil liquefaction susceptibility are applicable for relatively young Holocene soil deposits (<10,000 years) and do not consider the increase in cyclic resistance ratio over time. Particle rearrangement, interlocking and cementation are aging phenomenon that can cause increase in liquefaction resistance. For this study, in situ geotechnical data (cone penetration tests with pore pressure measurements and laboratory index tests) in the vicinity of prehistoric sandblows at Sampit and Gapway sites in the South Carolina Coastal Plain were used to reassess the back analysis of prehistoric earthquake magnitudes and maximum ground accelerations using newer, semi-empirical approaches than were used in previous analyses. The geotechnical data were used with paleoliquefaction evaluation methods that consider the effect of soil age and disturbance to estimate the magnitude and maximum ground acceleration needed for liquefaction at the time of the prehistoric earthquakes. Results show that the newer method for calculating acceleration is more conservative than the previously used approach. The difference is most significant for lower magnitudes. Calculated average values of age-adjusted magnitude range from 5 to 7.5 Richter and age-adjusted maximum ground acceleration for this variation of M range from 0.08 to 0.23g. 1 Ph.D Candidate, Dept. of Civil Engineering, University of South Carolina, Columbia, SC,USA 29208 2 Associate Professor, Dept. of Civil Engineering, University of South Carolina, Columbia, SC,USA 29208 Gheibi E, Gassman S L. Reassessment of prehistoric earthquake accelerations at Sampit and Gapway sites in South Carolina Coastal Plain. Proceedings of the 10 th National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Anchorage, AK, 2014.