1811–1812 New Madrid earthquakes

The 1811–1812 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 settlers. 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 50,000 square miles (130,000 km), and moderately across nearly 1 million sq mi (3 million km). The 1906 San Francisco earthquake, by comparison, was felt moderately over roughly 6,200 sq mi (16,000 km). The earthquakes were interpreted by Tecumseh's pan-Indian alliance, to mean that Tecumseh and his brother the Prophet must be supported.
The many more aftershocks include one magnitude 7 aftershock to the December 16, 1811, earthquake which occurred at 6:00 UTC (12:00 am local time) 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 (10:40 pm local time). Susan Hough, a seismologist of the United States Geological Survey, has estimated the earthquakes' magnitudes as around magnitude 7.
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:
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 (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.
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 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 to split the plate, but has remained as an aulacogen (a scar or weak zone) deep underground.
In recent decades, minor earthquakes have continued. The epicenters of over 4,000 earthquakes can be identified from seismic measurements since 1974, originating from the seismic activity of the Reelfoot Rift. Forecasts for the next 50 years estimate a 7–10% chance of a major earthquake like those of 1811–1812, and a 25–40% chance of a quake of magnitude 6 or greater.
In a report filed in November 2008, the U.S. Federal Emergency Management Agency warns that a serious earthquake in the New Madrid seismic zone could inflict "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 or greater magnitude quake would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure.
The quakes caused extensive changes to the region's topography. Subsidence, uplift, fissures, landslides and riverbank collapses were common. Trees were uprooted by the intense shaking; people drowned when subsided land flooded. Reelfoot Lake was formed in Tennessee by subsidence of 1.5 meters to 6 meters in some places. Lake St. Francis in eastern Arkansas was expanded by subsidence, with sand and coal being ejected from fissures in the adjacent swamps as water levels rose by 8 to 9 meters. Waves on the Mississippi River caused boats to wash ashore; river banks rose, sand bars were destroyed, and some islands completely disappeared. Sand blows occurred in Missouri, Tennessee, and Arkansas, covering farmland.
The continuous underlying rock mass, uninterrupted by fractures or faults, conducted the seismic waves from the earthquakes over great distances, with perceptible ground shaking as far away as Canada. Intense effects were widely felt in Illinois, Arkansas, Tennessee, Kentucky and Missouri.
The number of people who died is unknown; as a frontier area, the region was sparsely populated, and communications and records were poor. The predominantly wooden buildings resisted collapse, though the intense shaking caused many chimneys to fall, wood structures to crack, and trees to fall on buildings, particularly in the epicentral area during the first earthquake on December 16, 1811. A Methodist chaplain traveling with Andrew Jackson on his Natchez Expedition of 1813 recorded in his journal: "The fishers [fissures] produced in the earth about Madrid look awful on both sides of the River and the earth continues to shake at times, fears are ascertained that the worst is to come, it is said that there where about one thousand inhabitants in the Town of New Madrid previous to the Earth Quake – but many alarmed went off that at this time there only about 300."
Rated at VII on the Mercalli Intensity Scale, the New Madrid earthquakes remain the strongest recorded North American earthquakes east of the Rocky Mountains. The earthquakes strengthened the Shawnee prophet Tenskwatawa after the defeat at the Battle of Tippecanoe and the destruction of Prophetstown, with local Native Americans seeing it as a vindication of his teachings and of the warnings of his brother Tecumseh.
36°24′N 89°36′W﻿ / ﻿36.4°N 89.6°W﻿ / 36.4; -89.6