The New Madrid Fault could Reawaken at any Time
The New Madrid Fault could reawaken at any time and destroy
St. Louis, Missouri and
Memphis, Tennessee, like the
New Madrid Earthquake of 1811-12.
The New Madrid
Seismic Zone (pronounced /nuː ˈmædrɪd/), sometimes called the
New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes (earthquakes within a tectonic plate) in the southern and midwestern
United States, stretching to the southwest from
New Madrid, Missouri.
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 have been 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.
Geographic extent
The 150-mile (240 km) long fault system, which extends into five states, stretches southward from
Cairo, Illinois; through
Hayti,
Caruthersville and
New Madrid in Missouri; through
Blytheville into
Marked Tree in Arkansas. It also covers a part of
West Tennessee, near
Reelfoot Lake, extending southeast into
Dyersburg.
Most of the seismicity is located between 3 and 15 miles (4.8 and 24 km) beneath the
Earth's surface.
Earthquake history
The zone had four of the largest
North American earthquakes in recorded history, with moment magnitudes estimated to be as large as
8.0, all occurring within a three-month period between December 1811 and February 1812. Many of the published accounts describe the cumulative effects of all the earthquakes (known as the
New Madrid Sequence); thus finding the individual effects of each quake can be difficult.
Magnitude estimates and epicenters are based on interpretations of historical accounts and may vary.
Prehistoric earthquakes
Because uplift rates associated with large New Madrid earthquakes could not have occurred continuously over geological timescales without dramatically altering the local topography, studies have concluded that the seismic activity there cannot have gone on for longer than 64,
000 years, making the NMSZ a young feature, or earthquakes and the associated uplift migrate around the area over time, or that the NMSZ has short periods of activity interspersed with long periods of quiet. Archeological studies have found from studies of sand blows and soil horizons that previous series of very large earthquakes have occurred in the NMSZ in recent prehistory.
Based on artifacts found buried by sand blow deposits and from carbon-14 studies, previous large earthquakes like those of 1811--1812 appear to have happened around
AD 1450 and around
AD 900, as well as approximately
AD 300.
Evidence has been found for an apparent series of large earthquakes around
2350 BC. About 80 km southwest of the presently-defined NMSZ but close enough to be associated with the
Reelfoot Rift, near
Marianna, Arkansas, two sets of liquefaction features indicative of large earthquakes have been tentatively identified and dated to
3500 B.C. and
4800 B.C. These features were interpreted to have been caused by groups of large earthquakes timed closely together.
Dendrochronology (tree ring) studies conducted on the oldest bald cypress trees growing in Reelfoot Lake found evidence of the 1811--1812 series in the form of fractures followed by rapid growth after their inundation, whereas cores taken from old bald cypress trees in the
St. Francis sunklands showed slowed growth in the half century that followed 1812. These were interpreted as clear signals of the 1811--1812 earthquake series in tree rings. Because the tree ring record in Reelfoot Lake and the St. Francis sunklands extend back to
A.D. 1682 and A.D. 1321, respectively,
Van Arsdale et al. interpreted the lack of similar signals elsewhere in the chronology as evidence against large New Madrid earthquakes between those years and 1811.