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The Great Earthquake at New Madrid. A nineteenth-century woodcut from Devens' Our First Century (1877)
New Madrid fault and Earthquake prone region considered at high risk today.

The 1811-1812 New Madrid Earthquakes are the most intense intraplate earthquake series to have occurred in the contiguous United States in historic times, beginning with a very large earthquake on December 16, 1811. This earthquake, as well as the seismic zone of its occurrence, was named for the Mississippi River town of New Madrid, Louisiana Territory, now Missouri.

There are estimates that the earthquakes were felt strongly over roughly 130,000 square kilometers (50,000 square miles), and moderately across nearly 3 million square kilometers (1 million square miles). The historic 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 16,000 square kilometers (6,000 square miles).

Contents

Earthquakes

View to the southwest along the former riverbed of the Missouri River, just south of the Tennessee/Arkansas state line near Reverie, Tennessee and Wilson, Arkansas (2007)
  • December 16, 1811, 0815 UTC (2:15 a.m.); (M ~7.2 - 8.1[1]) 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 experienced level IX shaking on the Mercalli intensity scale. A seismic seiche propagated upriver and Little Prairie was heavily damaged by soil liquefaction[2]
  • December 16, 1811, 1415 UTC (8:15 a.m.); (M ~7.2 - 8.1) epicenter in northeast Arkansas. This shock followed the first earthquake by thirteen hours and was similar in intensity.[1]
  • January 23, 1812, 1500 UTC (9 a.m.); (M ~7.0 - 7.8[1]) epicenter in the Missouri Bootheel. The meizoseismal area was characterized by general ground warping, ejections, fissuring, severe landslides, and caving of stream banks. Johnson and Schweig attributed this earthquake to a rupture on the New Madrid North Fault. This may have placed strain on the Reelfoot Fault.[2]
  • February 7, 1812, 0945 UTC (4:45 a.m.); (M ~7.4 - 8.0[1]) 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, disrupted the Mississippi at Kentucky Bend, created a wave that propagated upstream, and caused the formation of Reelfoot Lake.[2]

The earthquakes were felt as far away as New York City and Boston, Massachusetts, where church bells rang.[3] There were reports that at one moment, Indians in the area looked up to where the Mississippi River was flowing.[citation needed]

Effects

From the historical record, it has been estimated that at least one of the quakes may have been as large as magnitude 8.0 on the moment magnitude scale. The estimates vary, because differences in models of seismic wave propagation in the eastern U.S. and different interpretations of epicenter locations.

There were numerous effects on the landscape in the most heavily affected area: a stream was impounded to form Reelfoot Lake, Tennessee; and the Mississippi River changed its course, creating numerous geographic exclaves, including the Kentucky Bend and the towns of Reverie and Corona, Tennessee, along the state boundaries defined by the river.

Some sections of the Mississippi River appeared to run backward for a short time. Sand blows were common throughout the area, and can still be seen from the air in cultivated fields. Church bells were reported to ring as far as Boston, Massachusetts and York, Ontario (now Toronto) and sidewalks were reported to have been cracked and broken in Washington, D.C.[4] There were also reports of toppled chimneys in Maine.

Eliza Bryan[5] in New Madrid, Territory of Missouri, wrote the following eyewitness account in March, 1812.

On the 16th of December, 1811, about two o'clock, A.M., we were visited by a violent shock of an earthquake, accompanied by a very awful noise resembling loud but distant thunder, but more hoarse and vibrating, which was followed in a few minutes by the complete saturation of the atmosphere, with sulphurious vapor, causing total darkness. The screams of the affrighted inhabitants running to and fro, not knowing where to go, or what to do - the cries of the fowls and beasts of every species - the cracking of trees falling, and the roaring of the Mississippi - the current of which was retrograde for a few minutes, owing as is supposed, to an irruption in its bed -- formed a scene truly horrible.

Disaster relief

A request, dated January 13, 1814, by William Clark, the governor of Missouri Territory (the territory was renamed soon after the quake to eliminate confusion with the new state of Louisiana), asked for federal relief for the "inhabitants of New Madrid County." This was possibly the first example of a request for disaster relief from the U.S. Federal government.

Geology

Reelfoot Rift

The Reelfoot Rift goes back about 750 million years, to when the entire landmass of the earth constituted a single supercontinent, designated now as Rodinia. An aulacogen was formed, now a subsurface feature called the Reelfoot Rift.

About 550 million years later, at the time of the supercontinent Pangaea, the fault zone again became active but no longer functioned as a constructive plate and remains in the same condition today. The earthquakes are therefore traced to seismic activity 5 to 25 kilometers (3-15 mi) below the crust of the earth.

Seismic Zone

The epicenters of over 4,000 earthquakes can be identified from seismic measurements taken since 1974. It can be seen that the earthquakes originate from the seismic activity of the Reelfoot Rift. The zone which is strongly colored in red on the map is called the New Madrid Seismic Zone.

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Recent earthquakes

4000 earthquake reports since 1974

The zone remains active today. In recent decades minor earthquakes have continued.[4] New forecasts estimate a 7 to 10 percent chance, in the next 50 years, of a repeat of a major earthquake like those that occurred in 1811-1812, which likely had magnitudes of between 7.5 and 8.0. There is a 25 to 40 percent chance, in a 50-year time span, of a magnitude 6.0 or greater earthquake.[6]

Understanding of this earthquake zone is growing slowly in comparison to awareness of the San Andreas fault.

Earthquake preparedness

The situation is more precarious than it was in 1811. The area is more densely populated, and many buildings have no earthquake resistant construction.

Active research in the region continues, with a goal of defining the risk of future earthquakes. A few emergency funds for earthquake victims have been founded. Measures are also being ordered to mitigate any natural disaster resulting from an earthquake; thus in the construction of dams, bridges, and highways, earthquake safety is particularly being taken into account.[7]

Gallery

See also

References

  • Jay Feldman. When the Mississippi Ran Backwards : Empire, Intrigue, Murder, and the New Madrid Earthquakes Free Press, 2005. ISBN 0743242785
  1. ^ a b c d Historic Earthquakes New Madrid Earthquakes 1811-1812 USGS
  2. ^ a b c 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)
  3. ^ [http://quake.wr.usgs.gov/prepare/factsheets/NewMadrid/ United States Geological Survey USGS
  4. ^ a b U.S. Geological Survey Fact Sheet-168-95 1995 The Mississippi Valley-"Whole Lotta Shakin' Goin' On"
  5. ^ Letter of Eliza Bryan found in Lorenzo Dow's Journal, Published By Joshua Martin, Printed By John B. Wolff, 1849, p.344. Accessed 2009-09-17. Archived 2009-09-21.
  6. ^ "USGS Release: Scientists Update New Madrid Earthquake Forecasts". Usgs.gov. 2003-01-13. http://www.usgs.gov/newsroom/article.asp?ID=215. Retrieved 2008-11-08. 
  7. ^ Hill, John R. Earthquake Near Evansville: Another Warning of Things to Come. http://igs.indiana.edu/geology/earthquakes/preparedness/index.cfm. 1 December 2009. WEB.

External links


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