EVOLUTION OF THE WOLF RIVER FLOOD PLAIN FROM 1940 TO 1988

Evidence for 1811-1812 earthquake liquefaction has been discovered along the Wolf River flood plain in the city of Memphis and Shelby County, Tennessee. There is concern about the possibility of liquefaction of this flood plain in future earthquakes. Geotechnical boring logs and water well logs were used to create structure contour maps of the base of the Pleistocene loess/top of the Pliocene-Pleistocene Upland Gravel (Lafayette Formation), and the bottom of the Upland Gravel/top of the Upper Claiborne Group. This mapping provides a three dimensional geologic framework for the Wolf River flood plain; however, the flood plain's surface is quite different today than it was in 1811-1812. To quantify how the Wolf River flood plain has changed over time, topographic data from 1940, 1965, a and 1988 were analyzed. Difference maps were created from 1940 to 1965, from 1965 to 1988, and from 1940 to 1988 to determine the degree of cut and fill that occurred within these time frames. These maps reveal accumulation and denudation along the flood plain between 1940 and 1988, mostly due to construction. Analyses allow a qualitative evaluation of the change in earthquake liquefaction potential as a consequence of cultural development of the Wolf River flood plain since 1940. The maps are also useful for evaluating flood potential and surface water/ground water connectivity.