The New Madrid Seismic Zone had four of the largest North American earthquakes in recorded history, with moment magnitudes estimated to be as large as 8.0, all occurring within a three-month period between December of 1811 and February of 1812.
Earthquakes that occur within the New Madrid Seismic Zone threaten parts of seven U.S. states: ILLINOIS, Indiana, Missouri, Arkansas, Kentucky, Tennessee, and Mississippi.
The New Madrid Seismic Zone, sometimes called the New Madrid Fault Line, (pronounced New MAH-drid) is a major seismic zone and a prolific source of intraplate earthquakes (earthquakes within a tectonic plate) in the Southern and Midwestern United States stretching to the southwest from New Madrid, Missouri.
The New Madrid fault system was responsible for the 1811–12 New Madrid Earthquakes and may have the potential to produce large earthquakes in the future. Since 1812 frequent smaller earthquakes were recorded for the area.
The 150 mi (240 km) long fault system, which extends into five states, stretches southward from Cairo, Illinois, through Hayti, Missouri, Caruthersville and New Madrid, through Blytheville, Arkansas, to Marked Tree. It also covers a part of west Tennessee, near Reelfoot Lake, extending southeast into Dyersburg.
http://en.wikipedia.org/wiki/New_Madrid_Seismic_Zone
P.S. My neighbors’ relatives lived in near present-day Pacaducah, KY in the far western part of the state. The western state border is marked by the Mississippi River. According to oral history passed down in their family, when the great quakes happened in 1811/1812 the movement of the earth was so drastic that the water of the mighty Mississippi River flowed backward!
Thanks for the link, and did you see my Comment #170?