The Enigma of the New Madrid Earthquakes of 1811-1812

Continental North America's greatest earthquake sequence struck on the western frontier of the United States. The frontier was not California but the valley of the continent's greatest river, the Mississippi, and the sequence was the New Madrid earthquakes of the winter of 1811--1812. Their described impacts on the land and the river were so dramatic as to produce widespread modern disbelief. However, geological, geophysical, and historical research, carried out mostly in the past two decades, has verified much in the historical accounts. The sequence included at least six (possibly nine) events of moment magnitude M 7 and two of M 8. The faulting was in the intruded crust of a failed intracontinental rift, beneath the saturated alluvium of the river valley, resulting in massive and extensive liquefaction. It involved at least six (and possibly more than seven) intersecting fault segments, one of which broke the surface as a thrust fault that ruptured the bed of the Mississippi in at least 2 (and possibly four) places.