The 1811–12 New Madrid earthquakes were a series of intense intraplate earthquakes beginning with an initial earthquake of moment magnitude 7.2–8.2 on December 16, 1811, followed by a moment magnitude 7.4 aftershock on the same day. Two additional earthquakes of similar magnitude followed in January and February 1812. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in recorded history. The earthquakes, 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 and now within the U.S. state of Missouri. The epicenters of the earthquakes were located in an area that at the time was at the distant western edge of the American frontier, only sparsely settled by European pioneers. Contemporary accounts have led seismologists to estimate that these stable continental region earthquakes were felt strongly throughout much of the central and eastern United States, across an area of roughly, and moderately across nearly 3 million km2. The 1906 San Francisco earthquake, by comparison, was felt moderately over roughly. The New Madrid earthquakes were interpreted variously by American Indian tribes, but one consensus was universally accepted; the powerful earthquake had to have meant something. For many tribes in Tecumseh's pan-Indian alliance, it meant that Tecumseh and his brother the Prophet must be supported.
The three earthquakes and their major aftershocks
December 16, 1811, 8:15 UTC : M 7.2–8.2, epicenter in what is now 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.
December 16, 1811 , 14:15 UTC : M 7.4, epicenter in northeast Arkansas. This shock followed the first earthquake by six hours and was similar in intensity.
January 23, 1812, 15:00 UTC : M 7.0–8.0, 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.
February 7, 1812, 9:45 UTC : M 7.4–8.6, epicenter near New Madrid, Missouri. The town of New Madrid was destroyed. In 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. Uplift along a segment of this reverse fault created temporary waterfalls on the Mississippi at Kentucky Bend, created waves that propagated upstream, and caused the formation of Reelfoot Lake by obstructing streams in what is now Lake County, Tennessee.
The many more aftershocks include one magnitude 7 aftershock to the December 16, 1811, earthquake which occurred at 6:00 UTC on December 17, 1811, and one magnitude 7 aftershock to the February 7, 1812, earthquake which occurred on the same day at 4:40 UTC. Susan Hough, a seismologist of the United States Geological Survey, has estimated the earthquakes' magnitudes as around magnitude 7.
Eyewitness accounts
, 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: Eliza Bryan in New Madrid, Territory of Missouri, wrote the following eyewitness account in March 1812: John Reynolds, the fourth governor of Illinois, among other political posts, mentions the earthquake in his biography My Own Times: Embracing Also the History of My Life : The Shaker diarist Samuel Swan McClelland described the effects of the earthquake on the Shaker settlement at West Union, Indiana, where the earthquakes contributed to the temporary abandonment of the westernmost Shaker community.
Geologic setting
The underlying cause of the 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 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 supercontinentRodinia in the Neoproterozoicera. 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 aulacogendeep underground. In recent decades, minor earthquakes have continued. The epicenters of over 4,000 earthquakes can be identified from seismic measurements taken since 1974. They originate from the seismic activity of the Reelfoot Rift. The zone, colored red on the map, is called the New Madrid Seismic Zone. 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 between 7.6 and 8.0. A 25 to 40% chance exists, 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.
