POSSIBLE QUATERNARY FAULTING BENEATH THE CITIES OF MEMPHIS AND GERMANTOWN, TENNESSEE

In excess of 600 geotechnical boring and water well logs have been geologically interpreted in Shelby County, Tennessee. Structure contour maps have been made of the top and bottom of the Pliocene-Pleistocene Lafayette Formation (Upland Gravel). A structure contour map has also been made of the top of the Eocene Memphis Sand by the USGS. These maps reveal ~100 feet of down-to-the-west displacement across an interpreted fault that trends N30E through eastern Memphis and Germantown in central Shelby County. The fault has a length of at least 10 miles, but its northern and southern limits have not yet been determined. We have tentatively named this structure the Ellendale fault. Seismic reflection lines also reveal down-to-the-west displacement. Since the Lafayette Formation is displaced, the faulting is probably Quaternary. A 1.64 feet (50 cm) wide liquefaction-induced sand dike was located along the strike of the Ellendale fault in the bank of the Wolf River and so it is possible that the fault was active in Holocene time. However, there is no surface scarp along the fault's trace. In view of these observations, the Ellendale fault may pose a seismic risk to the city of Memphis and Shelby County.