New Madrid Earthquake

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The New Madrid Earthquake, the largest earthquake ever recorded in the contiguous United States, occurred on February 7, 1812. (The largest recorded earthquake in the entire United States was the Alaskan Good Friday Earthquake on March 27, 1964.) It got its name from its primary location in the New Madrid Seismic Zone, near New Madrid, Louisiana Territory (now Missouri). This earthquake was preceded by three other major quakes: two on December 16, 1811, and one on January 23, 1812. These earthquakes destroyed approximately half the town of New Madrid. There were also numerous aftershocks in the area for the rest of that winter. There are estimates that the earthquakes were felt strongly over 50,000 square miles (130,000 km²), and moderately across nearly one million square miles. The historic San Francisco earthquake of 1906, by comparison, was felt moderately over 6,000 square miles (16,000 km²).

1 Effects
2 Reelfoot Rift: epicenter of the earthquake
3 New Madrid Seismic Zone
4 Gallery
5 See also
6 References
7 External links

Based on the effects of these earthquakes, it can be estimated that they had a magnitude of 8.0 on the Richter scale. As a result of the quakes, large areas sank into the earth, new lakes were formed (notably Reelfoot Lake, Tennessee), and the Mississippi River changed its course, creating Kentucky Bend. Nearby sections of the Mississippi River actually ran backwards for a short time. Sandblows were common throughout the area, and their effects can still be seen from the air in cultivated fields. Church bells were reported to ring in Boston, Massachusetts and sidewalks were reported to have been cracked and broken in Washington, D.C. .^[1]

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 Louisiana), 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 US Federal government, which would later become the job of the Federal Emergency Management Agency.

This area was much less developed at the time and a comparable event today would cause significant damage.

Reelfoot Rift: a still active fault

4000 earthquake reports since 1974

The Reelfoot Rift goes back about 750 million years, to when the entire landmass of the earth constituted a single supercontinent, designated now as Rodinia. At the time a constructive fault zone began to form, now called the Reelfoot Rift, but it failed, and the zone became inactive. About 550 million years later, at the time of the supercontinent called 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.

Main article: New Madrid 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.

The zone remains active today. In recent decades minor earthquakes have continued.^[1] 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.^[2]

The situation is more precarious than it was 200 years ago. The area is now more densely populated, and many buildings have no earthquake resistant construction. A few states have joined forces and founded a special institute for their earthquake zone, to prepare as well as possible for a major earthquake. The Mississippi River will probably present one of the incalculable problems. 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. Understanding of this earthquake zone is growing slowly in comparison to awareness of the San Andreas fault.

Almost 200 years after the earthquakes in 1811 and 1812, the course of the Mississippi River as it was before the events is still visible in the landscape of the affected areas today. Along and parallel to the Tennessee/Arkansas state line, the shrunk riverbed is still present.

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