The New Madrid Seismic Zone, sometimes called the New Madrid Fault Line, (pronounced New MAD-rid, short as in "mad" and accent on first syllable) 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 were recorded for the area.

Earthquakes that occur there potentially threaten parts of seven U.S. states: Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee, and Mississippi.

Geographic extent

The 150 mi (240 km) long fault system, which extends into five states, stretches southward from Cairo, Illinois, through Hayti, Missouri, Caruthersville and New Madrid, through Blytheville, Arkansas, to Marked Tree. It also covers a part of west Tennessee, near Reelfoot Lake, extending southeast into Dyersburg.

Most of the seismicity is located from 3 to 15 mi (5 to 25 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 greater than 8.0, all occurring within a 3 month period between December of 1811 and February of 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. (Abstract) Earthquake signals in tree-ring data from the New Madrid seismic zone and implications for paleoseismicity. RB Van Arsdale, DW Stahle, MK Cleaveland, and MJ Guccione. Geology; June 1998; v. 26; no. 6; p. 515-518; DOI: 10.1130/0091-7613(1998)026<0515:ESITRD>2.3.CO;2

December 25, 1699

The first known written record of an earthquake felt in the NMSZ was from a French missionary traveling up the Mississippi. At 1 PM, on Christmas Day, 1699, at a site near the present-day location of Memphis, the party was startled by a short period of ground shaking.

1811-1812 earthquake series

• December 16, 1811, 0815 UTC (2:15 a.m.); (MMS=8.2) moment magnitude scale; epicenter in northeast Arkansas; it caused only slight damage to man-made structures, mainly because of the sparse population in the epicentral area. The future location of Memphis, Tennessee was shaken at Mercalli level nine intensity. A seismic seiche propagated upriver and Little Prairie was destroyed by liquefaction.

At New Madrid, trees were knocked down and riverbanks collapsed. This event shook windows and furniture in Washington, D.C., rang bells in Richmond, Virginia, sloshed well water and shook houses in Charleston, South Carolina, and knocked plaster off of houses in Columbia, South Carolina. In Jefferson, Indiana, furniture moved and in Lebanon, Ohio, residents fled their homes. Observers in Herculaneum, Missouri, called it "severe" and claimed it had a duration of 10–12 minutes.

Aftershocks were felt every six to ten minutes, a total of 27, in New Madrid until what was called the Daylight Shock, which was of the same intensity as the first. Many of these were also felt throughout the eastern US, though with less intensity than the initial earthquake.

• December 16, 1811, the Daylight Shock, 1415 UTC (8:15 a.m.); (MMS=8.2) moment magnitude scale; epicenter in northeast Arkansas; This shock followed the first earthquake by six hours.

• January 23, 1812, 1500 UTC (9 a.m.); (MMS=8.1) moment magnitude scale; epicenter in the Missouri Bootheel. The meizoseismal area was characterized by general ground warping, ejections, fissuring, severe landslides, and caving of stream banks. Johnston and Schweig attributed this earthquake to a rupture on the New Madrid North Fault. This may have placed strain on the Reelfoot Fault.

• February 7, 1812, 0945 UTC (4:45 a.m.); (MMS=8.3) moment magnitude scale; epicenter near New Madrid, Missouri. New Madrid was destroyed. At St. Louis, Missouri, many houses were severely damaged, and their chimneys were toppled. This shock was definitively attributed to the Reelfoot Fault by Johnston and Schweig. It was uplift along this reverse fault segment, in this event, that created waterfalls on the Mississippi River, disrupted the Mississippi River at Kentucky bend, created a wave that propagated upstream and caused the formation of Reelfoot Lake.

The earthquakes were felt as far away as New York City and Boston, Massachusetts, where ground motion caused church bells to ring.

Hundreds of aftershocks followed over a period of several years. Aftershocks strong enough to be felt occurred until the year 1817. The largest earthquakes to have occurred since then were on January 4, 1843, and October 31, 1895, with magnitude estimates of 6.0 and 6.2 respectively.

This series of earthquakes caused permanent changes in the course of the Mississippi River, giving the illusion that it was flowing backward.

Modern activity

The biggest quake since 1811-1812 was a 6.6-magnitude quake on October 31, 1895, with an epicenter at Charleston, Missouri. The quake damaged virtually all buildings in Charleston, creating sand volcanoes by the city, cracked a pier on the Cairo Rail Bridge and toppled chimneys in St. Louis, Missouri, Memphis, Tennessee, Gadsden, Alabama and Evansville, Indiana.

The next biggest quake was a 5.4-magnitude quake (although it was reported as a 5.5 at the time) on November 9, 1968 near Dale, Illinois. The quake damaged the civic building at Henderson, Kentucky and was felt in 23 states. People in Boston said their building swayed. It is the biggest recorded quake with an epicenter in that state's recorded history.

Instruments were installed in and around the area in 1974 to closely monitor seismic activity. Since then, more than 4,000 earthquakes have been recorded, most of which were too small to be felt. On average, one earthquake per year is large enough to be felt in the area.

Geology

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 but has remained as an aulacogen (a scar or zone of weakness) deep underground. Another unsuccessful attempt at rifting 200 million years ago created additional faults, which made the area weaker. The resulting geological structures make up the Reelfoot Rift, and have since been deeply buried by younger sediments. But the ancient faults appear to have made the rocks deep in the Earth's crust in the New Madrid area mechanically weaker than much of the rest of North America.

This weakness, possibly combined with focusing effects from mechanically stronger igneous rocks nearby, allows the relatively small east-west compressive forces that exist in the North American plate to reactivate old faults, making the area prone to earthquakes.

Since other rifts are known to occur in North America's stress environment but not all are associated with modern earthquakes, (for example the Midcontinent Rift System that stretches from Minnesota to Kansas), other processes could be at work to locally increase mechanical stress on the New Madrid faults. Stress changes associated with bending of the lithosphere caused by the melting of continental glaciers at the end of the last Ice Age, has been considered to play a role , as well as downward pull from sinking igneous rock bodies below the fault. It has also been suggested that some form of heating in the lithosphere below the area may be making deep rocks more plastic, which concentrates compressive stress in the shallower subsurface area where the faulting occurs. There may be local stress from a change in the flow of the mantle beneath the NMSZ, caused by the sinking Farallon Plate, according to one model.

When epicenters of modern earthquakes are plotted on a map, three trends become apparent. First is the general northeast-southwest trend paralleling the trend of the Reelfoot Rift, in Arkansas, south of where the epicenters turn northwest. This is a strike-slip fault system parallel to the Reelfoot Rift. It is a dextral or right-handed fault because to an observer facing the fault, the other side would appear to move towards his right.

The second is the southeast to northwest trend that occurs just southwest of New Madrid. This trend is a stepover thrust fault known as the Reelfoot Fault, associated with the Tiptonville dome and the impoundment of Reelfoot Lake. Epicenter locations on this fault are more spread out because the fault surface is inclined and dips into the ground, towards the south, at around forty degrees. Motion (slip) is towards the northeast. Motion on this fault in the 1811-1812 series created waterfalls on the Mississippi.

The third trend, extending northeast from the northwestern end of the Reelfoot Fault is another right-handed strike-slip fault.

Potential for future earthquakes

In a report filed in November 2008, The U.S. Federal Emergency Management Agency warned that a serious earthquake in the New Madrid Seismic Zone could result in "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 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure.

The potential for the recurrence of large earthquakes and their impact today on densely populated cities in and around the seismic zone has generated much research devoted to understanding in the New Madrid Seismic Zone. By studying evidence of past quakes and closely monitoring ground motion and current earthquake activity, scientists attempt to understand their causes and recurrence intervals.

Iben Browning erroneous prediction of a big quake in 1990

Beginning in February 1989, business consultant Iben Browning predicted that there was a 50 percent probability of a magnitude 6.5 to 7.5 earthquake in the New Madrid area sometime between December 1 and 5, 1990. The United States Geological Survey requested an evaluation of the prediction by an advisory board of earth scientists, who concluded that "the prediction does not have scientific validity". However, this prediction was reported in the national and international media, and local agencies and citizens made preparations for the earthquake that was thought to be coming. No earthquake took place.

2009 Research indicating the fault may be shutting down

Compared to earthquake processes at plate boundaries, intraplate earthquakes, such as those that occur in the New Madrid Seismic Zone, are not well understood. One perplexing problem is the apparent lack of ground motion in the New Madrid zone. During the week of March 13, 2009, a research group based out of Northwestern University and Purdue University, funded by the United States Geological Survey, reported in the journal Science the results of an eight-year high resolution GPS survey of ground deformation along the faults implicated in the New Madrid earthquakes. The team were unable to detect any motion along the fault system, down to a resolution of 0.2mm/year, and concluded that the faults are not moving. This raised the possibility that the New Madrid system may be "shutting down" and that tectonic strain may now be accumulating elsewhere. Attempts to measure ongoing movement on the fault system have been equivocal at best, leaving the recurrence intervals of large earthquakes a subject of debate.

Research published in November 5, 2009 issue of Nature by researchers from Northwestern University and the University of Missouri indicates that recent quakes in the New Madrid seismic zone may be long-term aftershocks of the 1811-1812 earthquakes. The researchers say land around the fault is moving much slower than other earthquake prone areas such as California and consequently the energy is not building up to create a new quake but rather just adjusting to the previous quake. Land by the New Madrid zone is moving at no more than a year. This contrasts to the rate of slippage on the San Andreas Fault which averages up to a year across California.. Aftershocks on the San Andreas can occur up to about 10 years.

See also

• 1812 New Madrid earthquake
• Disaster preparedness
• Earthquake engineering
• Wabash Valley Seismic Zone
• Reelfoot Lake

References

1. http://www.ceri.memphis.edu/ Center for Earthquake Research and Information at the University of Memphis.
2. How old is the New Madrid Seismic Zone? Pratt, Thomas L. Seismological Research Letters, Volume 65, Number 2, April-June 1994. (PDF)
3. (Abstract) The Earthquake Potential of the New Madrid Seismic Zone Martitia P. Tuttle, Eugene S. Schweig, John D. Sims, Robert H. Lafferty, Lorraine W. Wolf, and Marion L. Haynes Bulletin of the Seismological Society of America (August 2002), 92(6):2080-2089
4. (Abstract) Evidence for New Madrid Earthquakes in A.D. 300 and 2350 B.C. Martitia P. Tuttle, Eugene S. Schweig, III, Janice Campbell, Prentice M. Thomas, John D. Sims, and Robert H. Lafferty, III. Seismological Research Letters, July/August 2005; 76: 489 - 501.
5. Very Large Earthquakes Centered Southwest of the New Madrid Seismic Zone 5,000-7,000 Years Ago. MP Tuttle, H Al-Shukri, H Mahdi. Seismological Research Letters, 2006
6. Jay Feldman. When the Mississippi Ran Backwards : Empire, Intrigue, Murder, and the New Madrid Earthquakes Free Press, 2005. ISBN 0743242785
7. USGS Circular 1083, "Responses to Iben Browning's prediction of a 1960 New Madrid, Missouri, earthquake".
8. The Enigma of the New Madrid Earthquakes of 1811-1812. Johnston, A. C. & Schweig, E. S. Annual Review of Earth and Planetary Sciences, Volume 24, pp. 339-384. Available on SAO/NASA Astrophysics Data System (ADS)
9. The New Madrid Earthquake. USGS Professional Bulletin 494. Myron Fuller (1912) (requires LizardTech online document viewer)
10. The New Madrid Earthquake. USGS Professional Bulletin 494. Myron Fuller (1912) (LizardTech online document)
11. USGS Circular 1083, "Responses to Iben Browning's prediction of a 1990 New Madrid, Missouri, earthquake".
12. http://quake.wr.usgs.gov/prepare/factsheets/NewMadrid/ United States Geological Survey USGS
13. http://earthquake.usgs.gov/regional/states/events/1811-1812.php#december_16 United States Geological Survey USGS
14. USGS Earthquake Hazards Program, Earthquake Report: Kentucky
15. (Abstract) Did deglaciation trigger intraplate seismicity in the New Madrid seismic zone? Balz Grollimund and Mark D. Zoback Geology (Boulder) (February 2001), 29(2):175-178
16. Sinking Mafic Body in a Reactivated Lower Crust: A Mechanism for Stress Concentration at the New Madrid Seismic Zone (Abstract) Fred F. Pollitz, Louise Kellogg and Roland Bürgmann. Bulletin of the Seismological Society of America; December 2001; v. 91; no. 6; p. 1882-1897; DOI: 10.1785/0120000277
17. [1] (Abstract) Liu, L., and M. D. Zoback (1997), Lithospheric strength and intraplate seismicity in the New Madrid seismic zone, Tectonics, 16(4), 585–595.
18. Descent of the ancient Farallon slab drives localized mantle flow below the New Madrid seismic zone, Geophys. Res. Lett., Forte, A. M., J. X. Mitrovica, R. Moucha, N. A. Simmons, and S. P. Grand (2007) Geophys. Res. Lett., 34, L04308, doi:10.1029/2006GL027895.
19. http://news.yahoo.com/s/nm/20081120/us_nm/us_earthquake_study;_ylt=AkY.pkcM1pDbSKQ7ePCNGu2s0NUE "Government warns of 'catastrophic' U.S. quake" - Reuters
20. http://esciencenews.com/articles/2009/03/13/new.madrid.fault.system.may.be.shutting.down "New Madrid Fault System May Be Shutting Down" Eureka! Science News
21. New Madrid fault system may be shutting down - physorg.com – March 13, 2009

• USGS New Madrid
• U.S. Geologic Survey site discusses the New Madrid seismic zone.
• Uncovering Hidden Hazards in the Mississippi Valley
• Central US Earthquake Consortium
• U. Memphis, TN, Center for Earthquake Research and Information (CERI) comprehensive references for the 1811–1812 earthquakes
• Links to eyewitness descriptions of the three 1811-12 earthquakes, and results of the earthquakes as seen in photographs of 1904.
• Your Fault, My Fault, and the New Madrid Fault
• Space geodetic evidence for rapid strain rates in the New Madrid seismic zone of Central USA (PDF)

Further reading

• Boyd, K.F. (1995). Geomorphic evidence of deformation in the northern part of the New Madrid seismic zone [U.S. Geological Survey Professional Paper 1538-R]. Washington, D.C.: U.S. Department of the Interior, U.S. Geological Survey.
• Langenheim, V.E. (1995). Gravity of the New Madrid seismic zone : a preliminary study [U.S. Geological Survey Professional Paper 1538-L]. Washington, D.C.: U.S. Department of the Interior, U.S. Geological Survey.
• Odum, J.K., et al. (1995). High-resolution, shallow, seismic reflection surveys of the northwest Reelfoot rift boundary near Marston, Missouri [U.S. Geological Survey Professional Paper 1538-P]. Washington, D.C.: U.S. Department of the Interior, U.S. Geological Survey.
• Potter, C.J., et al. (1995). Structure of the Reelfoot-Rough Creek rift system, fluorspar area fault complex and Hicks dome, southern Illinois and western Kentucky : new constraints from regional seismic reflection data [U.S. Geological Survey Professional Paper 1538-Q]. Washington, D.C.: U.S. Department of the Interior, U.S. Geological Survey.
• Rodriguez, B.D. (1995). Axial structures within the Reelfoot rift delineated with magnetotelluric surveys [U.S. Geological Survey Professional Paper 1538-K]. Washington, D.C.: U.S. Department of the Interior, U.S. Geological Survey.
• Stephenson, W.J., K.M. Shedlock, and J.K. Odum. (1995). Characterization of the Cottonwood Grove and Ridgely faults near Reelfoot Lake, Tennessee, from high-resolution seismic reflection data [U.S. Geological Survey Professional Paper 1538-I]. Washington, D.C.: U.S. Department of the Interior, U.S. Geological Survey.

External links

• Center for Earthquake Research and Information at the University of Memphis. Recent central U.S. earthquakes