Between Little Rock, Ark., and Memphis, Tenn., scientists have found evidence of an earthquake source capable of magnitude 7 or greater earthquakes located at the southwestern end of the ancient Reelfoot Rift. This is the same geologic structure that hosts the New Madrid seismic zone which is responsible for the major earthquakes that occurred in the midcontinent almost 200 years ago.
The geologic proof includes large, visible sand blows formed by strong ground shaking, and subsurface geophysical imaging of faulting nearby. Field observations and radiocarbon dating suggest that the sand blows formed as the result of two to four earthquakes between 4,800 and 10,000 years ago.
The New Madrid fault system was responsible for the 1811–1812 New Madrid earthquakes and may have the potential to produce large earthquakes in the future. Since 1812 frequent smaller earthquakes were recorded in the area.
Earthquakes that occur in the New Madrid Seismic Zone potentially threaten parts of seven American states: Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee and Mississippi.