THE GEOARCHEOLOGICAL RECORD OF PALEOEARTHQUAKES IN THE NEW MADRID SEISMIC ZONE, CENTRAL UNITED STATES

From numerous historical accounts, it is well known that a sequence of very large (M 7.5-8) earthquakes produced by the New Madrid seismic zone led to great changes in the landscape of the lower Mississippi River valley in 1811-12, including uplift and subsidence of large areas, changes in river courses, failure of bluffs and river banks, and other ground failures related to liquefaction of sediment. This natural disaster had a huge impact on pioneers that had recently settled the floodplain of the Mississippi River. Similar New Madrid events about A.D. 1450, A.D. 900, and 2350 B.C. are recorded in the geoarcheological record of the region encompassing the New Madrid seismic zone. Earthquake-induced liquefaction features, including sand-blow deposits and sand dikes, are the telltale signs of strong ground shaking. In the New Madrid region, sand-blow deposits are underlain and overlain by Native American horizons and features. Artifacts and organic material in the cultural horizons and features have helped to date the liquefaction features and thus the earthquakes. Lateral and vertical displacements resulting from liquefaction have confounded the archeological record; but the sand blows deposited above archeological sites have helped to protect them from plowing and grading. The impact of pre-1811 New Madrid events on native people is difficult to assess; however changes in ceramic technology, settlement patterns, and ceremonial attention to sand blows coincident with the earthquakes suggests a strong relationship.

The 2350 B. C. event has been documented under a small mound, the base of which was made of yellow imported clay and centered on the dike.

The A.D. 900 event has been the best documented at more than 20 sites and appears to have had far reaching effects on the cultures of the region. The event occurred at the transition from the Woodland period to the Mississippian. There is a major change to shell-tempered pottery, as well as changes in the settlement patterns. There is some evidence of ceremonialism oriented toward the sand blows.

The A.D. 1450 event coincides with the abandonment of the Missouri Bootheel and some adjacent portions of Arkansas by the Mississippian Culture. In 1541 De Soto sent an expedition north from north of Memphis and they describe the area having many pondy swamps. A description not unlike the landscape described by Fuller a century after the 1811-12 events.