LIQUEFACTION POTENTIAL MAPPING IN MEMPHIS/SHELBY COUNTY, TENNESSEE

RIX, G.J., and ROMERO-HUDOCK, S., School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355, glenn.rix@ce.gatech.edu.

The City of Memphis, Tennessee, and surrounding Shelby County constitute a large, urban area that is prone to damage from earthquakes in the New Madrid Seismic Zone (NMSZ). Surficial deposits in the Memphis/Shelby County area include Holocene artificial fill, Holocene alluvium deposits along river channels, Pleistocene loess and terrace deposits in the interfluve regions, and Pliocene-Pleistocene Upland gravel deposits known as the Lafayette Formation. Many of these deposits are susceptible to liquefaction. Previous studies have focused on the susceptibility of geologic deposits to liquefaction and did not consider the seismic demand required to initiate liquefaction or the severity of liquefaction. In this study, liquefaction potential maps are developed for six, 7.5-minute quadrangles in the Memphis/Shelby County area. Seismic demand is derived from a complementary study focused on ground motion estimates in the Memphis/Shelby County area. Liquefaction resistance is derived from available standard penetration test (SPT) and cone penetration test (CPT) profiles. For each profile, the factor of safety against liquefaction is determined using the "simplified procedure". The liquefaction potential index (LPI) is calculated for each profile based on the factor of safety against liquefaction. The LPI results are then aggregated according to the surficial geology. The liquefaction potential maps show the probability of "moderate" and "major" liquefaction within each geologic unit for a given earthquake scenario. As an example of the use of this approach, we prepared liquefaction hazard maps for the study area for a M_w = 7.7 scenario earthquake on the southwest arm of the New Madrid fault. The maps give the probabilities of exceeding LPI values of 5 and 15, which correspond to "moderate" and "major liquefaction-induced damage, respectively. The probability values are binned in increments of 20 percent to better reflect the uncertainties in this approach.