Liquefaction susceptibility mapping in the city of Memphis and Shelby County, Tennessee

摘要

Earthquake-induced sand dikes have been identified in cut banks of the Wolf and Loosahatchie Rivers in the city of Memphis and Shelby County, Tennessee. Most of the dikes are near the mouths of these rivers within the city limits of Memphis, hut one dike occurs 36 km upstream in the hank of the Wolf River in Collierville. The dikes range in width from 1 to 50 cm and at Nome localities can he traced vertically as much as 4 m from their source bed to within 50 cm of the flood plain surface. The age of the dikes is unknown, but they are interpreted to be from the great 1811-1812 New Madrid earthquakes because they are locally buried by historical sediments containing bricks. The larger number of dikes and upstream extent of liquefaction along the Wolf River suggests that liquefaction susceptibility is greater in the Wolf River flood plain than in other flood plains in Shelby County. This greater liquefaction susceptibility of the Wolf River flood plain appears to he due to the sand in its basal point-bar sequence and a relatively thin overbank silt/clay cap.Geologic and geologically based liquefaction susceptibility maps (1:24 000) were made of the Memphis Northwest and Collierville 7.5' quadrangles of Shelby County. The liquefaction susceptibility maps show very high susceptibility for Mississippi, Wolf, and Loosahatchie River flood plains, high susceptibility in areas of artificial fill on these three flood plains, moderate susceptibility along other flood plains and terraces in these quadrangles, and low susceptibilities in the interfluve areas.