Influence of Assumed Groundwater Depth on Mapping Liquefaction Potential

Groundwater depth is a critical parameter in assessing regional liquefaction potential. Uncertainties associated with groundwater depth are usually perva-sive because of natural variability and spatial separa-tion between data points. These uncertainties often lead to erroneous or doubtful assessments of liquefaction potential. In an attempt to provide more credible estimates of liquefaction potential across a sizable urban area, this study sought to estimate the threshold groundwater depths that could be expected to trigger liquefaction in the St. Louis, MO, metro area, which was damaged by the 1811–1812 New Madrid earth-quakes. We used liquefaction potential indexes (LPIs). 5 and. 15 as the thresholds for moderate and severe liquefaction risks, respectively. The threshold ground-water depth for triggering liquefaction was evaluated using standard penetration test data and a scenario involving an M7.5 earthquake with a peak ground acceleration of 0.20 g. The threshold groundwater depths then were geostatistically contoured and com-pared with accepted groundwater level scenarios to map the corresponding liquefaction risk. This study revealed that Holocene alluvium in East St. Louis generally exhibits deeper threshold groundwater depths than do the mean groundwater levels and appears to be more prone to liquefaction