The New Madrid fault is not a very well known fault, even though it should be for a multitude of reasons. It is still very much active and dangerous because of the geography of it (causes it to spread to more states), and low frequency of feelable earthquakes.
The New Madrid Fault is 20 miles long and starts from around Charleston, Missouri, goes through New Madrid, and ends at Marked Tree, Arkansas. The fault ruptures about 200 times a year, but only has one you can feel annually. The last earthquake on the New Madrid Fault over 7.5 on the Richter scale was in 1811-1812, and was actually a collection of over 200 earthquakes. Twelve of these were strong enough to cause church bells to ring on the east coast!
The New Madrid fault was formed when Pangea broke up, and is actually where North America tried to split in two. Magma came up and formed plutons, such as the Devils Tower (Not made by the creation of the New Madrid Fault) in Wyoming, and these tend to destabilize a seismic area even more. It created sand blows otherwise known as sand volcanoes, in which the sand came from a reservoir of sand that formed when the Atlantic Ocean receded.
The last earthquake that was over 4.0 from the new Madrid fault was in 1996, and had a magnitude of 4.3 and was felt in Missouri, Arkansas, Tennessee, Kentucky, Illinois and Mississippi. High magnitude earthquakes have a low frequency of occurrence so most people are unprepared for a damaging one. Earthquakes over 5.0 occur once a decade, for example.
The New Madrid Fault should be more respected and much, much more feared for the above reasons. Its low frequency of strong earthquakes is the main reason that causes it to be so dangerous. Were you aware of the great New Madrid Fault, or were you ignorant, like everyone else?
Information collected from the following sites: http://www.scchealth.org/docs/ems/docs/prepare/newMadrid.html by the St. Charles County Department of Community Health & The Environment, and http://www.showme.net/~fkeller/quake/origins.htm by Stanford University