The other Big One

The responsible for the New Madrid Seismic Zone are embedded in a subsurface geological feature known as the Reelfoot Rift that formed during the breakup of the   in the   (about 750 million years ago). The resulting system failed to split the continent, but has remained as an  (a scar or zone of weakness) deep underground, and its ancient faults appear to have made the Earth's crust in the New Madrid area mechanically weaker than much of the rest of North America.

In a report filed in November 2008, the U.S. warned that a serious earthquake in the New Madrid Seismic Zone could result in "the highest economic losses due to a natural disaster in the United States," further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kansas, Kentucky, Mississippi, Missouri, Oklahoma, Texas, and particularly Tennessee, where a 7.7 magnitude quake would cause damage to tens of thousands of structures affecting, , and other vital. The earthquake is expected to also result in many thousands of fatalities, with more than 4,000 of the fatalities expected in Memphis alone.

1811–12 earthquake series

 * December 16, 1811, 0815 UTC (2:15 a.m.); (M ~7.5) epicenter in northeast Arkansas, probably on the Cottonwood Grove fault; it caused only slight damage to man-made structures, mainly because of the sparse population in the epicentral area. The future location of was shaken at Mercalli level nine intensity. A seismic  propagated upriver and Little Prairie was destroyed by . Local uplifts of the ground and the sight of water waves moving upstream gave observers the impression that the Mississippi River was flowing backwards.At New Madrid, trees were knocked down and riverbanks collapsed. This event shook windows and furniture in Washington, D.C., rang bells in Richmond, Virginia, sloshed well water and shook houses in Charleston, South Carolina, and knocked plaster off of houses in Columbia, South Carolina. In Jefferson, Indiana, furniture moved and in Lebanon, Ohio, residents fled their homes. Observers in Herculaneum, Missouri, called it "severe" and said it had a duration of 10–12 minutes.s were felt every 6-10 minutes, a total of 27, in New Madrid until what was called the Daylight Shock, which was of the same intensity as the first. Many of these were also felt throughout the eastern US, though with less intensity than the initial earthquake.
 * December 16, 1811, sometimes termed the "Dawn Shock" or "Daylight Shock", 1315 UTC (7:15 am); (M ~ 7) epicenter in northeast Arkansas.
 * January 23, 1812, 1515 UTC (9:15 am); (M ~7.3) epicenter around New Madrid, although this is disputed. This was probably the smallest of the three main shocks, but resulted in widespread ground deformation, landslides, fissuring, and stream bank caving in the . Johnston and Schweig attributed this earthquake to a rupture on the New Madrid North Fault. A minority viewpoint holds that this earthquake's epicenter was in southern Illinois. A 2011 expert panel urged further research to clarify this point, stating that the Illinois hypothesis would mean that an extended section of fault exists, perhaps still loaded and capable of hosting a great earthquake in the future.
 * February 7, 1812, 0945 UTC (3:45 am); (M ~7.5) epicenter near New Madrid, Missouri. This was the largest event in the series, and it destroyed the town of New Madrid. At, many houses were severely damaged, and their chimneys were toppled. It appears to have occurred on Reelfoot fault, a segment that crosses under the Mississippi River just south of  and continues to the east as the Lake County Uplift. In this event, uplift along the fault created temporary waterfalls on the , created a wave that propagated upstream, and caused the formation of  by damming streams.