A Deformation-Based Approach for Mapping Earthquake-Induced Liquefaction Hazard

A deformation-based approach for mapping earthquake-induced liquefaction hazard has been developed that utilizes recently generated predictive relationships for shear-strain potential. These new relationships are used to calculate "Displacement Potential Index" given induced cyclic stress ratio and normalized fines-corrected standard penetration resistance. Conventional liquefaction hazard mapping is based on qualitative assessments of surface deposits, their geomorphology, environment and recency of deposition, and past performance from post-earthquake investigations. This new method is a more quantitative, deformation-based approach that emphasizes the severity of ground failure rather than mere likelihood of liquefaction. These new methods are being investigated for use in improving delineation of California's regulatory liquefaction hazard zones. Over 650 boring logs have been analyzed for 18 Quaternary geologic map units in a pilot study covering a portion of the southern San Francisco Bay Area in Santa Clara County. A sufficient number of boring logs were available for nine of the Quaternary units to permit reclassification into four liquefaction susceptibility units, for which parametric modeling was performed and ground deformation hazard mapped over the test area. Pilot study results show good agreement with historical occurrences of liquefaction.