Liquefaction Probability Analysis of Quaternary Deposits in the Greater Charleston, South Carolina Area

摘要

The 1886 Charleston earthquake caused substantial liquefaction-induced ground failure throughout the Charleston, South Carolina region. The investigation is based on an analysis of seismic cone penetration test profiles for 228 sites in the sand deposits, and 90 sites in the clayey deposits. A review of major mapped ground failures and observed disturbances along rail lines following the 1886 Charleston earthquake (Mw ~7.0) is also presented. Liquefaction susceptibility and liquefaction potential are expressed in terms of the liquefaction potential index (LPI). LPI is used because 1) it offers a single value for a site, 2) it is one of the best single-value approaches currently available, and 3) it can be compared with results of other researchers. The effect of aging processes or diagenesis is considered through a correction factor (KDR) that is based on the ratio of measured shear-wave velocity (VS) to estimated VS. Results of the liquefaction susceptibility assessment indicate there is little to no significant relationship between LPI and distance to the 1886 seismic source, or with distance to nearest perennial stream for the clayey deposits.;Liquefaction probability curves are expressed as functions of peak ground acceleration, earthquake magnitude, and probability that LPI is greater than or equal to a threshold value for surface manifestation of liquefaction at level ground sites. The results indicate that among the six sand deposits, the three youngest exhibit the highest probability for a given level of ground shaking. Likewise among the five clayey deposits, the youngest is shown to have the highest probability for a given earthquake load, while the four older clayey units display lower probabilities similar to each other. The liquefaction probability curves developed for all deposits generally agree well with the recorded observations of ground failure following the 1886 earthquake. Model probability curves are also generated for the clayey deposits assuming relevant combinations of depth to groundwater and depth to top of Cooper Marl. The liquefaction probability curves may be used to create regional hazard maps, but should not replace site-specific evaluations.