New Madrid Seismic Zone: The 1811–1812 Quakes and Hazard Today
The New Madrid seismic zone is an earthquake zone in the central Mississippi River Valley, in the area of northeastern Arkansas, southeastern Missouri, western Tennessee and Kentucky, and southern Illinois. It produced three principal earthquakes of magnitude 7.5, 7.3 and 7.5 between December 16, 1811, and February 7, 1812. The USGS estimates a 7 to 10 percent chance of a repeat of one of those earthquakes in 50 years, and a 25 to 40 percent chance of a magnitude 6 or larger.
Where is the New Madrid seismic zone?
The New Madrid seismic zone lies along the Mississippi River in the middle of the North American plate, far from any plate boundary. The USGS calls it the most seismically active area of the United States east of the Rockies.
The ground failures of 1811 and 1812 covered the heart of the zone. The USGS catalog says the most seriously affected region stretched from Cairo, Illinois, to Memphis, Tennessee, and from Crowleys Ridge, Arkansas, to Chickasaw Bluffs, Tennessee. That area covered 78,000 to 129,000 square kilometers (about 30,000 to 50,000 square miles).
In its fact sheet on New Madrid hazard, the USGS says a repeat could produce similar ground failures in northeastern Arkansas, southeastern Missouri, western Tennessee and Kentucky, and southern Illinois. It names Memphis, St. Louis and Little Rock among the cities that would see damage.
What happened in the 1811–1812 New Madrid earthquakes?
Between December 1811 and February 1812, the zone produced three principal earthquakes and a large aftershock, all magnitude 7 or larger. The magnitudes below are the values the USGS adopted for its 2014 National Seismic Hazard Map as the best average of five scientific studies.
| Date (UTC) | Location (USGS catalog) | Magnitude | Range in studies |
|---|---|---|---|
| December 16, 1811 | Northeastern Arkansas | 7.5 | 6.8 to 8.1 |
| December 16, 1811, about 5 hours later | Western Tennessee (now considered an aftershock) | 7.0 | Not listed |
| January 23, 1812 | North of New Madrid, Missouri | 7.3 | 6.9 to 7.8 |
| February 7, 1812 | Western Tennessee | 7.5 | 7.2 to 8.0 |
The USGS notes that the second shock on December 16 is now treated as an aftershock, so the principal earthquakes are counted as three. Each principal shock is the largest earthquake on record in its state: Arkansas, Missouri and Tennessee.
The sequence was long. According to the USGS catalog, seismologist Otto Nuttli counted more than 200 aftershocks of magnitude 4 or greater between December 16, 1811, and March 15, 1812. About 1,800 earthquakes of roughly magnitude 3 to 4 occurred in the same period.
How far away were the New Madrid earthquakes felt?
Shaking strong enough to alarm people, rated above intensity V on the Modified Mercalli scale, covered about 2.5 million square kilometers (about 965,000 square miles). The USGS catalog entry for December 16, 1811 says that area reached from Canada to New Orleans, and from the headwaters of the Mississippi River to the Atlantic Ocean. Chimneys fell as far away as Cincinnati, Ohio, and St. Louis, Missouri.
The USGS adds that the area of strong shaking was two to three times larger than in the 1964 Alaska earthquake and 10 times larger than in the 1906 San Francisco earthquake. The USGS also notes that, because of the crustal structure of the central US, shaking from earthquakes there is felt much farther away than from similar-sized earthquakes in the West. Our guide to magnitude vs intensity explains how intensity is mapped.
The land changed shape. The USGS describes uplift, sinking ground, fissures, sand blows and large landslides. Reelfoot Lake in Tennessee subsided by 1.5 to 6 meters (5 to 20 feet). The February 7, 1812, shock destroyed the town of New Madrid.
Why are there earthquakes in the middle of the continent?
New Madrid earthquakes happen inside a tectonic plate, not at its edge. The USGS explains that at plate boundaries like coastal California and Alaska, deformation can be measured continuously at the surface. Inside a plate, some models predict little surface deformation between large earthquakes.
GPS measurements since about 1996 have shown little movement across part of the zone. A 2006 USGS workshop of experts reviewed that data and did not find it a convincing reason to lower the hazard assessment, given the other evidence.
That other evidence is in the soil. Sand blows form when buried sand and water erupt to the surface during violent shaking. The USGS says large, widespread prehistoric sand blows show earlier clusters of big earthquakes around A.D. 1450, A.D. 900 and 2350 B.C. The zone has produced sequences of major earthquakes, including several of magnitude 7 to 8, over the past 4,500 years.
What does the USGS say about the hazard today?
The USGS assessment rests on three things: the geologic record, the 1811–1812 accounts and continuing small and moderate earthquakes. The agency notes the rate of smaller earthquakes is not decreasing, as it would if they were only aftershocks of 1811–1812.
| Earthquake | USGS estimate |
|---|---|
| Average time between 1811–1812-type earthquakes | About 500 years |
| Chance of an earthquake like one of the 1811–1812 shocks in 50 years | About 7 to 10 percent |
| Chance of a magnitude 6 or larger in 50 years | 25 to 40 percent |
These estimates come from USGS Fact Sheet 2009-3071, published in August 2009. In it, the USGS lists effects a repeat could bring: liquefaction across the Mississippi River floodplain, landslides along river bluffs, damaged bridges and impassable roads such as Interstate 55. It singles out the Memphis metropolitan area, with more than one million people, as likely to be severely affected.
How can you check earthquakes in the New Madrid region?
- See our live lists of USGS earthquakes in Missouri, Tennessee and Arkansas for the last 24 hours, 7 days and 30 days.
- Open the USGS event page of any quake to see its magnitude type and depth. Our guide on how to read a USGS earthquake report explains each field.
- Add a “Did You Feel It?” report on the USGS event page if you felt shaking; those reports build the intensity map.
Our pages show official USGS data only and are not warnings. For preparedness guidance, follow your state and local emergency management agencies.
Bottom line
The New Madrid seismic zone sits in the middle of the continent but has produced magnitude 7.3 to 7.5 earthquakes, most recently in 1811–1812. Shaking from central US earthquakes travels far, which is why chimneys fell in Cincinnati and St. Louis. The USGS puts the 50-year chance of a repeat at 7 to 10 percent and the chance of a magnitude 6 or larger at 25 to 40 percent.
FAQ
Which states are in the New Madrid seismic zone?
The USGS names northeastern Arkansas, southeastern Missouri, western Tennessee and Kentucky, and southern Illinois as the areas where a repeat would cause ground failures like those of 1811–1812. Shaking in 1811–1812 was felt far beyond those states.
How strong were the New Madrid earthquakes?
The USGS lists the three principal shocks at magnitude 7.5 (December 16, 1811), 7.3 (January 23, 1812) and 7.5 (February 7, 1812). Studies have estimated values from 6.8 to 8.1, so these are best averages.
Is the New Madrid seismic zone still active?
Yes. The USGS calls it the most seismically active area of the United States east of the Rockies, with continuing small and moderate earthquakes.
Where can I compare New Madrid with other large US earthquakes?
Our list of the largest earthquakes in US history ranks New Madrid against Alaska, Cascadia and California events using the USGS catalog.