EARTHQUAKE LIQUEFACTION SUSCEPTIBILITY MAPPING IN MEMPHIS, TN

Geologic mapping in the city of Memphis and Shelby County, Tennessee, have identified numerous earthquake liquefaction sand dikes in Holocene flood plain sediments of the Wolf River, minor liquefaction at the mouth of the Loosahatchie River, and no liquefaction along Nonconnah Creek. The Wolf River has a thin silt overbank sequence (2.5-6 m) overlying point bar sands, the Loosahatchie has a thick overbank sequence (7.5-9 m) overlying point bar sands, and the Nonconnah Creek flood plain is dominantly silt. The liquefaction variation is believed due to differing flood plain lithologies and thicknesses. Specifically, Nonconnah Creek has no liquefiable sand and the Loosahatchie River has a thick overbank silt layer that apparently inhibits liquefaction. Thus, liquefaction susceptibility mapping in Memphis differentiates among the Holocene river flood plains.

The liquefaction was probably caused by the great 1811-1812 New Madrid earthquakes. Based on its lithology and liquefaction history, the Wolf River flood plain is mapped as being highly susceptible to future liquefaction. However, this flood plain has undergone extensive cut and fill changes due to river channelization and construction since 1811-1812 that will probably influence its behavior in future earthquakes.