NEW GEOLOGIC MAPS IN THE MEMPHIS, TENNESSEE AREA HELP ASSESS THE POTENTIAL FOR EARTHQUAKE-INDUCED GROUND FAILURE
Silty loess, 4.5-16 m thick, and local, thin, silty colluvium mantle the hilly upland adjacent to the Mississippi River. We infer these deposits, if at less than field saturation during strong earthquake shaking, are unlikely to liquefy because no paleoliquefaction features were seen in the loess and engineering laboratory studies support this inference. However, sandy alluvial deposits that underlie floodplains of the Mississippi River and the tributary Wolf River are more likely to liquefy. Structures founded on these deposits incur risk. We conclude this based on relict sand blow features on the floodplain of the Mississippi and sand dikes in banks (viewed in cross section) of the Wolf River. The dikes were probably feeder conduits of sand blows or paleoliquefaction features, formed during the large New Madrid, MO earthquakes of 1811-1812, or an earlier or later earthquake, such as the >6 magnitude quake centered 60 km northwest of Memphis near Marked Tree, AR in 1843. This work was funded by the National Cooperative Geologic Mapping and Earthquake Hazard Reduction Programs of the USGS.