Archaeological and Pedological Evidence for Large Prehistoric Earthquakes in the New-Madrid Seismic Zone, Central United-States

Prehistoric liquefaction features have been identified by careful observation of their structural and stratigraphic relations to Native American occupation horizons and their subtle soil characteristics. The ages of these liquefaction features have been estimated from radiocarbon dating of wood associated with the features and Native American artifacts found within bounding occupation horizons. At three sites near Blytheville, Arkansas, in the central part of the New Madrid seismic zone, one sand-blow crater formed between A.D. 800 and 1400, two sand-blow deposits formed between A.D. 800 and 1670, and three, possibly four, sand dikes formed since 4035 B.C. Where not found in association with Native American occupation horizons and artifacts, prehistoric liquefaction features can be difficult to distinguish from features that formed during the great New Madrid earthquakes of A.D. 1811 and 1812. This raises the possibility that prehistoric liquefaction features may have been misinterpreted during previous studies in the area. Nevertheless, a paleoearthquake chronology is beginning to emerge for the New Madrid seismic zone. Our findings are consistent with paleoseismological studies in the northern part of the seismic zone and suggest a recurrence interval of hundreds of years for earthquakes large enough to induce liquefaction in this region (M greater than or equal to 6.4). By mapping the age distribution of liquefaction features, a more accurate assessment of the long-term earthquake potential of the region will be possible.