Why study the New Madrid Seismic Zone?
For the last 40 years, the New Madrid area has been the most seismically active region in the United States east of the Rocky Mountains, and it has a history of large magnitude earthquakes going back several thousand years. Though no knowledge of an imminent large earthquake exists, the USGS has serious concerns about the potential repeat of a destructive earthquake in the New Madrid Seismic Zone, like the remarkable earthquake sequence that occurred in the winter of 1811–1812. This sequence of earthquakes was felt 800 to 1000 miles away along the Eastern Seaboard. President James Madison felt these earthquakes in Washington D.C., and wrote about the shaking he felt in a letter to Thomas Jefferson.
Geologic evidence from sand blows shows that sequences of large earthquakes with magnitudes ranging from 7 to 8 also occurred in this region in about 1450 A.D., 900 A.D., and 2300 B.C. The geologic evidence indicates that these earthquakes were large with strong aftershocks that produced prolonged and severe ground motions in the area that is now home to several million people.
Similar risk exists today
A repeat of the 1811–1812 earthquakes in the New Madrid Seismic Zone today threatens northern Alabama, northeastern Arkansas, southern Illinois, southern Indiana, western Kentucky, northern Mississippi, southeastern Missouri, and western Tennessee. Recent USGS projections place the likelihood of a magnitude 6 or higher earthquake at about 25 to 50 percent over the next 50 years, and the likelihood of a magnitude 7 or higher earthquake at 10 percent.
With large cities such as Memphis, St. Louis, Little Rock, and Nashville experiencing strong shaking from a large-scale New Madrid earthquake, understanding earthquake hazards helps communities prepare for them, thereby reducing losses and speeding recovery.
Faults sometimes bring together rocks with different magnetic properties. These variations in magnetic properties produce very small magnetic fields that can be measured with low-flying aircraft, allowing USGS scientists the ability to map and characterize faults even though they may be completely hidden by vegetation or young sediments.
