The effects of the quakes were extensive and dramatic. Aftershock activity continued over the next decade. Aftershocks strong enough to be felt extended through 1817. An estimated 1,800 additional aftershocks took place during the same period. More than 200 aftershocks ranging from large to moderate were reported between December 1811 and March 1812. In addition to the main shocks, 4 aftershocks estimated at greater than 6.0 occurred between Decemand February 1812.

The area of strong shaking was approximately 10 times that of the Great 1906 San Francisco Earthquake. The area of damage is estimated at 600,000 square kilometers the quakes were felt over an area of approximately 5,000,000 square kilometers. The main shocks were felt as far away as the Gulf Coast, East Coast, and Quebec. As there were no seismograph stations in the region at that time, magnitude estimates vary widely (from 7.7 to 8.1) based on interpretation of journal accounts, damage reports, and descriptions of effects from that time.

The 3 main shocks were estimated at magnitudes 7.7, 7.5, and 7.7. What many refer to as the Great New Madrid Earthquake, was actually a seismic event made up of 3 major quakes, followed by thousands of aftershocks, ranging from strong damaging quakes and diminishing to weaker quakes that lasted for years after the main shocks. More About the 1811-1812 New Madrid Seismic Event Today approximately 270 seismic stations monitor the region in a cooperative network. In 1811, there were no seismographs in the region until the first seismograph was installed at St. Some estimates project that damage in Missouri alone could reach $6 billion for a major earthquake. Urban development, along with the increase in population, elevates the potential for fatalities and injuries, and damage to infrastructure by a similar event in modern times. Today an estimated 11 to 12 million live in the St. Sparsely populated and developed then, there were approximately 5,700 residents in St. In the 200 years since 1811, changes to the areas that would be affected by major quake activity in the zone have been drastic. It was felt over all or portions of 23 states and at some places in Canada.

Near Charleston, 4 acres of ground sank and a lake was formed. Cairo, Illinois, and Memphis, Tennessee, also suffered significant damage. The Charleston quake, the strongest since 1811, damaged every building in the commercial area of Charleston. Two of the strongest include a magnitude 6.0 on Janucentered near Marked Tree, Arkansas, and a magnitude 6.6 on Octocentered near Charleston, Missouri. Damaging quakes have occurred in the New Madrid Zone since then. Current research has indicated large quake activity going back at least 5,000 years. Evidence of similar activity has been found, dated around 900 A.D., and again in 1450 A.D. EvidenceĪpparently, 'New Madrid' sized events have occurred before 1811. On the list for the continental 48 states, the New Madrid main shocks are ranked #5, 6, and 7. On the USGS list of the 20 largest earthquakes in all 50 United States, the 3 main shocks are ranked #18, 19, and 20 (Alaska dominates the top of the list). To date, the earthquakes of 1811-1812 remain 1 of the most remarkable seismic events in history. For a quake of 6.0 to 7.0, the probability is 28-46% over the next 50 years. The USGS has projected that for an earthquake of magnitude 7.5 to 8.0, the probability for occurrence is approximately 7-10% over the next 50 years. Based on evidence of quake activity found in geological features, scientists estimate that the average interval between magnitude 7.0 quakes or greater is approximately 500 years. The likelihood or probability can be calculated from patterns of recurrence in the past. Shake and damage areas are up to 20 times larger than similar West Coast quakes.Įarthquakes cannot be predicted. The harder, colder, drier, less fractured crust in the central U.S generates greater shaking over larger areas than quakes of comparable magnitude in the west. What has been learned in studies there may not apply here.Īnother contrast is due to a difference in geological characteristics. is being deformed / strained slowly in contrast to conditions in the west. Unlike the West Coast where major quake activity is more predictable based on measured movement at tectonic plate boundaries, New Madrid is located near the center of the North American Plate.

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