1812 New Madrid earthquake
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The 1811 or 1812 New Madrid Earthquake is the most intense intraplate earthquake series to have occurred in the contiguous United States, beginning with an initial pair of very large earthquakes on December 16, 1811. These earthquakes as well as the seismic zone of their occurrence were 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).
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[edit] Earthquakes
- December 16, 1811, 0815 UTC (2:15 a.m.); (MMS=8.2[1]) 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 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.); (MMS=8.2[3]) 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[4]) 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. 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.); (MMS=8.3[5]) 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. [2]
The earthquakes were felt as far away as New York City and Boston, Massachusetts, where church bells rang.[6]
[edit] Effects
From the historical record, it has been estimated that at least one of them may have had a magnitude of 8.0 on the Moment Magnitude scale, though the numbers vary, because of such things as differences in models of seismic wave propagation in the Eastern US as well as 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 a geographic exclaves, including Kentucky Bend, 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.[7] There were also reports of toppled chimneys in Maine.
[edit] 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.
[edit] Geology
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 called 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.
[edit] 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.
[edit] Recent earthquakes
The zone remains active today. In recent decades minor earthquakes have continued.[7] 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.[8]
Understanding of this earthquake zone is growing slowly in comparison to awareness of the San Andreas fault.
[edit] 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.
[edit] Gallery
 Reelfoot Rift and NMSZ |
View to the southwest along the former riverbed of the Mississippi River, south of the Tennessee/Arkansas state line near Reverie, Tennessee and Wilson, Arkansas (2007) |
 View to the northeast |
 Damage-range comparison between a moderate New Madrid zone earthquake (1895, magnitude 6.8), and a similar Los Angeles event (1994, magnitude 6.7). |
[edit] See also
[edit] References
- United States Geological Survey (2003-10-15). "USGS Earthquake Hazards Program: 1811 - 1812 Earthquakes in the New Madrid Seismic Zone". Retrieved 2005-05-03.
- Jay Feldman. When the Mississippi Ran Backwards : Empire, Intrigue, Murder, and the New Madrid Earthquakes Free Press, 2005. ISBN 0743242785
- ^ USGS Circular 1083, "Responses to Iben Browning's prediction of a 1960 New Madrid, Missouri, earthquake".
- ^ 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)
- ^ USGS Circular 1083, "Responses to Iben Browning's prediction of a 1990 New Madrid, Missouri, earthquake".
- ^ USGS Circular 1083, "Responses to Iben Browning's prediction of a 1990 New Madrid, Missouri, earthquake".
- ^ USGS Circular 1083, "Responses to Iben Browning's prediction of a 1990 New Madrid, Missouri, earthquake".
- ^ http://quake.wr.usgs.gov/prepare/factsheets/NewMadrid/ United States Geological Survey USGS
- ^ a b U.S. Geological Survey Fact Sheet-168-95 1995 The Mississippi Valley-"Whole Lotta Shakin' Goin' On"
- ^ "USGS Release: Scientists Update New Madrid Earthquake Forecasts". Usgs.gov. 2003-01-13. http://www.usgs.gov/newsroom/article.asp?ID=215. Retrieved on 2008-11-08.
[edit] External links
- USGS: NMSZ since 1811; also theories
- Synopsis, along with eyewitness accounts
- New Madrid seismic zone
- The New Madrid Fault Zone
- The Enigma of the New Madrid Earthquakes of 1811-1812. Johnson, A.C. and Schweig, E.S. (1996) Annual Review of Earth and Planetary Sciences, Volume 24, pp. 339–384. SAO/NASA Astrophysics Data System (ADS)
