Geology, Geotechnical Engineering, and Natural Hazards of Memphis, Tennessee, USA

The generally flat landscape of the Memphis, TN, area hides a fascinating geologic history. Cambrian rifting resulted in the concealed faults of the Reelfoot rift, currently the active component of the New Madrid 1 Seismic Zone, lying immediately northwest of the city. Memphis also sits within the Mississippi Embayment. Subsidence of the embayment brought about deposition of the thick Late Cretaceous and Cenozoic sedimentary sequence underlying the city. This sequence provides one of the finest groundwater aquifers in the world, the Memphis Sand. Pliocene ancestral Ohio River alluvium (Upland Complex) is an excellent source of sand and gravel for the region. Plio-Pleistocene fluvial degradation by the Mississippi River and its tributaries, in addition to deposition of Pleistocene loess sheets, have produced the subtle topography of Memphis and Shelby County. Memphis geology makes geotechnical engineering design challenging because loess is highly sensitive to disturbance. Exploratory sampling techniques tend to cause disturbance to loess during sampling and sample extraction. Thus, conventional sampling techniques yield variable engineering property test results (e.g., strength and compressibility). The city of Memphis and Shelby County have together become a major commodities distribution center for the United States, North America, and the global economy. The principal natural hazards are the frequent severe weather and the prospect of a repeat of the > 7M 1811-1812 New Madrid earthquakes. These unavoidable exposures to severe weather, urban and riverine flooding, and earthquakes combined with social conditions tend to amplify the consequences of hazard events.