Evidence for large New Madrid earthquakes about A.D. 0 and 1050 B.C., central United States

Investigations of earthquake-induced liquefaction features, including sand blows and their feeder dikes, in the New Madrid seismic zone have led to the discovery of a previously unrecognized earthquake that occurred in A.D. 0+ or -200 yr. In addition, new findings support another New Madrid earthquake sequence in 1050+ or -250 yr B.C. The studies, which consisted of geological and geophysical reconnaissance, archaeological surveys and excavations, as well as paleoseismic trenching and logging, focused on two sites located in northeastern Arkansas. Characteristics of the liquefaction features, their stratigraphic relations with cultural horizons and artifacts, and radiometric dating support the timing of the liquefaction events. With the addition of the A.D. 0 and 1050 B.C. events to the New Madrid earthquake chronology (A.D. 1811-1812, A.D. 1450, A.D. 900, A.D. 0, 1050 B.C., and 2350 B.C.), a recurrence time of approximately 1100 yrs is estimated for the period between 2350 B.C. and A.D. 900, whereas a previously established recurrence time of approximately 500 yrs remains unchanged for the period between A.D. 900 and 1811. The findings of sand blows indicative of additional New Madrid earthquakes between 2350 B.C. and A.D. 900 suggest that the New Madrid earthquake chronology may still be incomplete, and if so, an 1100-yr recurrence time may be an overestimate for this time period.