New Madrid Seismic Zone Produced Historic Earthquakes in 1811 and 1812

The New Madrid seismic zone has recently garnered attention as speculation about the possibility of a major earthquake runs rampant and the bicentennial of the great earthquakes of 1811-1812 approaches. The New Madrid seismic zone averages a number of earthquakes each week but they are usually too small in magnitude to be noticed or felt. The southern Illinois, southeast Missouri, western Kentucky region in the Midwest is located on the New Madrid seismic zone and the fault falls into parts of Tennessee and Arkansas. The New Madrid holds the record for the largest earthquakes in North America after a devastating series of quakes that occurred in the early 1800s, before the area was heavily populated.

These earthquakes occurred during the winter of 1811 and 1812. This series of quakes and aftershocks occurred near New Madrid, Missouri along this Midwestern fault zone which would later be named the New Madrid fault or the New Madrid seismic zone.

The first massive earthquake happened just after 2 a.m. on December 16, 1811. This earthquake was believed to have been an 8.0 in magnitude or larger.

For perspective, the October, 1989 Loma Prieta earthquake that struck the San Francisco and Monterey Bay areas in California, was a 6.9 magnitude quake. The earthquake that struck Haiti in January, 2010 was a 7.0 magnitude and the February, 2010 quake that struck near Maule, Chile was an 8.8. The largest recorded earthquake in the world struck Chile in May 1960 and was registered as a 9.5 magnitude.

Reports state that this New Madrid quake in 1811 was felt as far away as Pittsburgh, Pennsylvania and Norfolk, Virginia--a distance of more than 600 miles. Chimneys were reported to have been toppled in Louisville, Kentucky and President Thomas Jefferson was awakened in his bed in Washington D.C.

Two more large, similarly-sized shocks struck later that morning and several much smaller shakes were felt.

Two other principal aftershocks occurred a few weeks later on January 23 and February 7, 1812. Experts believe the third quake that struck on February 7 was the largest of the three main quakes (which means it was larger than the initial 8.0 quake that struck on December 16). The estimates for magnitude of these quakes are based upon expert analysis of damage records.

The USGS website states that it is estimated the initial quake from December 16 spawned countless aftershocks that continued to rattle the region as late as 1817.

The area where these earthquakes were centered had a very small population which meant that damage to structures was minimal. However, damage to the land was immense.

Reelfoot Lake in Tennessee was formed when one of the quakes shoved a portion of the earth upward to create the Tiptonville Horst and the area that would become Reelfoot sank. Reports of huge fissures in the ground are recorded and some of these fissures were so large that men on horseback were unable to cross them. Farmland was damaged by excessive ruts and fissures caused by the earthquakes.

The damage from this series of quakes led the United States Congress to pass the very first disaster relief act in 1815 to aid landowners in the area who had lost the use of their land due to the New Madrid quakes. Landowners were provided with compensation of land in other areas.

Extensive damage along rivers and waterways was also reported, including the disappearance of islands, the caving in of riverbanks and even reports that the Mississippi River flowed backward for a time during the quaking and created areas of waterfalls. Sand blows (also called sand boils) occurred in the area and some may still be seen in the area today and in historic pictures on the USGS website. Sand blows happen when sand and water blow out of the ground during an earthquake--much like a geyser. Sand blows are caused by shallow depth liquefaction.

The New Madrid seismic zone is close to another fault area--the Wabash Valley seismic zone, which was responsible for a 5.4 magnitude quake in April, 2008. This quake was centered near Olney in southeastern Illinois.

Could earthquakes of this magnitude or greater occur today in the New Madrid seismic zone and is the risk for the area greater because of the proximity of the Wabash Valley fault? The possibility of a New Madrid earthquake has been debated for many years among residents and experts. According to the Southern Illinois University at Carbondale Department of Geology website, a seismic event of the same magnitude as the 1811-1812 earthquakes occurring today in the New Madrid seismic zone would cause a substantial loss of life and property damage would most likely range in the billions of dollars.

This area is now heavily populated and includes the cities of Memphis, Tenn., St. Louis, Mo., Paducah, Ky., Little Rock, Ark. and Evansville, Ind. Many experts believe that the New Madrid Fault Zone is overdue for a large earthquake and USGS experts have projected that there is a 25-40 percent chance that the New Madrid fault zone will have a major earthquake of magnitude 6.0 or greater within the next 50 years (USGS Fact Sheet FS-131-02 - October, 2002).

Sources:
http://www.geology.siu.edu/quakes/nmadrid.html
http://earthquake.usgs.gov/earthquakes/states/events/1811_overview.php
http://earthquake.usgs.gov/aboutus/nepec/meetings/10Nov_Pasadena/USGS_FS_2009-3071_CUS_hazards.pdf