Recent earthquake reminder that New Madrid Fault still active
Posted: Feb 24, 2013
This graphic shows the earthquakes in the New Madrid Fault Zone from 1974 to today. Source: CERI
The Reelfoot Rift as depicted below the surface. Source: USGS.
Center of 2/23/13 3.6 mag. earthquake. From Google Maps.The 3.6 mag. earthquake was centered just southwest of Trumann in Poinsett County and was felt across a dozen or so counties in Arkansas, Missouri, Tennessee, and Mississippi. It was one of hundreds of earthquakes that shake the region each year.
The New Madrid Seismic Zone (NMSZ) runs 150 miles from Cairo, IL to Marked Tree, AR and is described as a series of faults called the Reelfoot Rift. The rift formed about 500 million years ago when scientists believe the continent tried to split apart. It didn't happen, but what was left was a weakened spot in the bedrock below. Thanks to the Mississippi River, the faults were covered up by sand and other sediment. The NMSZ also differs from what many consider as traditional fault zones because it is not along a plate boundary where to pieces of earth's crust are rubbing against each other.
Some of the largest earthquakes to ever shake the United States happened in the winter of 1811-12. The earthquakes shook bells in the northeastern U.S., created Reelfoot Lake in Tennessee, and caused the Mississippi River to temporarily run backwards near New Madrid, MO.
Since the 1812 earthquakes, the largest earthquake to strike the region was a 6.3 mag. near Marked Tree in 1843. While there are many small earthquakes that still shake the region, there is discontent among the scientific community whether the next big one is going to strike.
Seismologists have warned for years the area is not prepared for a moderate to strong earthquake. Many of the buildings, especially those older than 40 years, are not built to seismic standards. In Memphis for example, the I-40 bridge (Hernando De Soto Bridge) was built in 1973. That "new" bridge is much newer than the I-55 bridge (Memphis and Arkansas Bridge) built in 1949. It is unknown if either bridge would survive an earthquake like those that shook 200 years ago. Many of the buildings in downtown Memphis, Jonesboro, and Blytheville are much older and even on historic significance lists. Many of the newer buildings are constructed to seismic code, meaning they are reinforced to withstand a moderate to strong earthquake.
Those familiar with the earthquakes in the region warn residents not to worry about "the next big one", but a moderate 5.5 - 6.6 magnitude earthquake, which is much more likely to happen and will do significant damage to the infrastructure. Buildings, bridges, and other standing structures near the epicenter will likely see significant damage. The best advice is to be prepared with a plan and survival kit, just in case.
For More Information:
USGS New Madrid Fault Zone
Center for Earthquake Research and Information (CERI) at the University of Memphis
Central U.S. Earthquake Consortium
Helicorder Displays in the Mid-South
http://www.kait8.com/story/21318497/recent-earthquake-reminder-that-new-madrid-fault-still-active
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