QUATERNARY FAULTING IN MEMPHIS, TENNESSEE

Over 600 wells and geotechnical borings in the city of Memphis and Shelby County, TN, were geologically interpreted. In these wells and borings we identified the base of the Pleistocene loess/top of the Pliocene-Pleistocene Upland Gravel (Lafayette Formation) and the bottom of the Upland Gravel. Structure contour maps of the top and bottom of the Upland Gravel reveal an apparent down-to-the-west fault (herein called the Ellendale fault) with approximately 30 m of structural relief that strikes N25E located in the eastern portion of Memphis and northwestern Germantown. The Ellendale fault coincides with a deeper unnamed fault mapped in the underlying Eocene section by previous investigators. Until removed by 2001 Spring flooding, a 50 cm wide liquefaction-induced sand dike was exposed along the surface trace of the Ellendale fault in the north bank of the Wolf River. To better image the Ellendale fault, we shot a 260 m long high-resolution S-wave reflection line along the southern bank of the Wolf River. The line was located to cross the western edge of the Ellendale fault zone and was centered on the opposing bank sand dike location. Preliminary interpretation of the reflection line revealed an anticline at the base of the Wolf River alluvium and down-to-the-west displacement of the underlying Eocene strata near the line's center. Based on these preliminary data we believe that the Ellendale fault has been active during the Quaternary and therefore may pose a seismic threat to the city of Memphis and Shelby County.