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The 1811–1812 New Madrid earthquakes / / were an intense intraplate earthquake series beginning with an initial pair of very large earthquakes on December 16, 1811. These earthquakes remain the most powerful earthquakes to hit the eastern United States in recorded history. These events, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, then part of the Louisiana Territory, now within Missouri.
There are estimates that the earthquakes were felt strongly over roughly 130,000 square kilometers (50,000 sq mi), 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 km2 (6,200 sq mi).
Susan Hough, a seismologist of the United States Geological Survey (USGS), has recently estimated the earthquakes' magnitudes as "right around magnitude 7. Possibly a bit below, possibly a bit above, but not as big as 7.5."
John Bradbury, a Fellow of the Linnean Society, was on the Mississippi on the night of December 15, 1811, and describes the tremors in great detail in his Travels in the Interior of America in the Years 1809, 1810 and 1811, published in 1817.
After supper, we went to sleep as usual: about ten o'clock, and in the night I was awakened by the most tremendous noise, accompanied by an agitation of the boat so violent, that it appeared in danger of upsetting ... I could distinctly see the river as if agitated by a storm; and although the noise was inconceivably loud and terrific, I could distinctly hear the crash of falling trees, and the screaming of the wild fowl on the river, but found that the boat was still safe at her moorings.
By the time we could get to our fire, which was on a large flag in the stern of the boat, the shock had ceased; but immediately the perpendicular banks, both above and below us, began to fall into the river in such vast masses, as to nearly sink our boat by the swell they occasioned ... At day-light we had counted twenty-seven shocks.
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.
John Reynolds (February 26, 1788 – May 8, 1865) who was the 4th governor of Illinois, among other political posts, mentions the earthquake in his biography My Own Times: Embracing Also the History of My Life (1855):
On the night of 16th November [sic], 1811, an earthquake occurred, that produced great consternation amongst the people. The centre of the violence was in New Madrid, Missouri, but the whole valley of the Mississippi was violently agitated. Our family all were sleeping in a log cabin, and my father leaped out of bed crying aloud "the Indians are on the house" ... We laughed at the mistake of my father, but soon found out it was worse than the Indians. Not one in the family knew at the time that it was an earthquake. The next morning another shock made us acquainted with it, so we decided it was an earthquake. The cattle came running home bellowing with fear, and all animals were terribly alarmed on the occasion. Our house cracked and quivered, so we were fearful it would fall to the ground. In the American Bottom many chimneys were thrown down, and the church bell in Cahokia sounded by the agitation of the building. It is said the shock of an earthquake was felt in Kaskaskia in 1804, but I did not perceive it. The shocks continued for years in Illinois, and some have experienced it this year, 1855.
The Shaker diarist Samuel Swan McClelland described the effects of the earthquake on the Shaker settlement at West Union (Busro), Indiana, where the earthquakes contributed to the temporary abandonment of the westernmost Shaker community.
Sand blows were common throughout the area, and can still be seen from the air in cultivated fields. The shockwaves propagated efficiently through the firm midwestern bedrock, with residents as far away as Pittsburgh, Pennsylvania, and Norfolk, Virginia, awakened by intense shaking. 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.
A request, dated January 13, 1812, by William Clark (famous for his exploration of the American West with Meriwether Lewis and the Corps of Discovery from 1803 to 1805), then the governor of the Louisiana Territory (the territory was renamed the Missouri Territory soon after the quake to eliminate confusion with the new state of Louisiana), asked for federal relief for the "inhabitants of New Madrid County."
Whereas the Catalogue of miseries and afflictions, with which it has pleased the Supreme Being of the Universe to visit the inhabitants of the earth there are none more
truly awful and destructive than Earthquakes ... The inhabitants of the late District now County of New Madrid, in this Territory, have lately been visited with several calamities of this kind, which have deluged large portions of their country and involved in the greatest distress many families, whilst others have been entirely ruined ... In the opinion of the said General Assembly provisions ought to be made by law for or cashiered to the said inhabitants relief, either out of the public fund or in some other way as may can meet to the cost demand availability of the General Government.
This is possibly the very first request that the U.S. Federal Government had received for aid from one of its territories.
The earthquakes helped bring to justice the murderers of George Lewis (commonly known as "Slave George"). George was slain on the night of December 15–16, 1811 by two nephews of Thomas Jefferson, Lilburn Lewis and Isham Lewis, who were also relatives of Meriwether Lewis. After killing him with an axe in front of other slaves, George's owners intended to burn his remains, but the first New Madrid earthquake interrupted their effort, and so the corpse was interred in a brick chimney. The murder might well have escaped discovery by authorities, except that the January 23 and February 7 quakes caused the chimney to partially collapse, exposing George's remains. Lilburn and Isham Lewis were quickly investigated, arrested and charged. Lilburn killed himself; Isham escaped from jail and probably died during the War of 1812.
The underlying cause of New Madrid earthquakes is not well understood, but modern faulting seems to be related to an ancient geologic feature buried under the Mississippi River alluvial plain, known as the Reelfoot Rift.
The New Madrid Seismic Zone (NMSZ) 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 Michigan 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 right-lateral strike-slip fault system parallel to the Reelfoot Rift.
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. Slip is towards the northeast. Motion on this fault in the 1811–1812 series created waterfalls on the Mississippi.
The third line, extending northeast from the northwestern end of the Reelfoot Fault is another right-lateral strike-slip fault, termed New Madrid North.
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 colored in red on the map is called the New Madrid Seismic Zone.
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.
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 prompted research devoted to understanding 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.
The lack of apparent land movement along the New Madrid fault system has long puzzled scientists. In 2009 two studies based on eight years of GPS measurements indicated that the faults were moving at no more than 0.2 millimeters (0.0079 in) a year. In contrast, the rate of slippage on the San Andreas Fault averages as much as 37 mm (1.5 in) a year across California.