The underlying cause of the earthquakes is not well understood, but modern faulting seems to be related to an ancient geologic feature buried under the Mississippi River
alluvial plain, known as the Reelfoot Rift. The New Madrid seismic zone is made up of reactivated
faults that formed when what is now North America began to split or
rift apart during the breakup of the supercontinent
Rodinia in the
Neoproterozoic era (about 750 million years ago). Faults were created along the rift, and
igneous rocks formed from
magma that was being pushed towards the surface. The resulting rift system failed to split the plate, but has remained as an
aulacogen (a scar or weak zone) deep underground. In recent decades, minor earthquakes have continued. The epicenters of over 4,000 earthquakes can be identified from seismic measurements since 1974, originating from the seismic activity of the Reelfoot Rift. USGS Forecasts made in 2003 estimated a 7–10% chance of a major earthquake like those of 1811–1812, and a 25–40% chance of a quake of magnitude 6 or greater, within the next 50 years. In a report filed in November 2008, the U.S.
Federal Emergency Management Agency warns that a serious earthquake in the New Madrid seismic zone could inflict "the highest economic losses due to a
natural disaster in the United States", further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and particularly Tennessee, where a 7.7 or greater magnitude quake would cause damage to tens of thousands of structures affecting
water distribution,
transportation systems, and other vital infrastructure. ==Aftermath==