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1812 New Madrid earthquake: Map

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New Madrid fault and Earthquake prone region considered at high risk today.


The 1811 and 1812 New Madrid Earthquakes are 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 Madridmarker, Louisiana Territory, now Missourimarker.

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).

Earthquakes





  • December 16, 1811, 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 Bootheelmarker. 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.


  • 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, Missourimarker, 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 Lakemarker.


The earthquakes were felt as far away as New York Citymarker and Boston, Massachusettsmarker, where church bells rang.

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 Lakemarker, Tennesseemarker, and the Mississippi River changed its course, creating a geographic exclaves, including Kentucky Bendmarker, 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, Massachusettsmarker and York, Ontario marker and sidewalks were reported to have been cracked and broken in Washington, D.C.marker There were also reports of toppled chimneys in Maine.

Eliza Bryan 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 retrogade 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 Louisianamarker), 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 Riftmarker 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.

Recent earthquakes

4000 earthquake reports since 1974
The zone remains active today. In recent decades minor earthquakes have continued. 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.

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

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.

Gallery

 Image:NMSZ_Erdbeben.jpg|Reelfoot Rift and NMSZ
 Image:Reverie_ms_river_s.jpg|View to the southwest along the former riverbed of the Mississippi River, south of the Tennessee/Arkansas state line near Reverie, Tennesseemarker and Wilson, Arkansasmarker (2007)
 Image:Reverie_ms_river_n.jpg|View to the northeast
 Image:NMSZ_Vergleich.jpg|Damage-range comparison between a moderate New Madrid zone earthquake (1895, magnitude 6.8), and a similar Los Angeles event (1994, magnitude 6.7).


See also



References



  • Jay Feldman. When the Mississippi Ran Backwards : Empire, Intrigue, Murder, and the New Madrid Earthquakes Free Press, 2005. ISBN 0743242785




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