Earthquake dangers from the New Madrid fault.
With the recent earthquakes in Haiti, New Zealand and Japan, Americans may wonder if or when such a disaster will or might happen closer to home. While most Americans know of the potential for earthquakes along the West Coast’s San Andreas Fault, fewer realize that a major fault line lies near Memphis, Tenn.
The New Madrid (MAH dred) fault is one of the most dangerous in the world. Located beneath the upper end of the Mississippi delta, the fault extends from Cairo, Ill., to Marked Tree, Ark., a distance of 130 miles (220 km). Geologists and other scientists have studied the New Madrid for many years.
According to the United States Geological Survey (USGS), the New Madrid area experienced a series of earthquakes in 1811 and 1812 that were among the strongest documented in the United States since its settlement by Europeans. The geographic area affected by the intense shaking during the quakes was two to three times larger than that of the 1964 Alaska earthquake and 10 times larger than that of the 1906 San Francisco earthquake.
Exact magnitudes of the New Madrid earthquakes are impossible to know, as there were no seismographs in North America in the early 1800s. The region around the New Madrid fault had relatively low density of European population at the time, but there were many written eyewitness accounts. Evidence of the intensity of the New Madrid quakes is present today and warns of widespread devastation, should a similar event reoccur.
Scientists have pieced together estimated magnitudes for the New Madrid quakes using journals, newspaper reports and other accounts of the ground shaking, subsidence and change to the landscape. They estimate the quakes were between magnitude 7.0 and 8.0, causing extreme ground movements both vertically and horizontally.
In northwest Tennessee, Reelfoot Lake formed when an area 20 miles (32 km) long subsided during one of the quakes and the depression filled with water from the Mississippi River. The Mississippi reportedly reversed its direction of flow for several hours immediately following the quake. Church bells rang in Montreal, Canada, and the tremors were felt in Boston.
The location of the New Madrid fault creates the potential for very destructive quakes. The most phenomenal ground motion from earthquakes normally occurs on unconsolidated sediments, such as sand, silt and gravel. Such loose earth materials have no solid material holding them together. The materials overlying the New Madrid fault are soft unconsolidated deltaic sediments deposited by the Mississippi, whose delta extends from Cairo, Ill., to the Gulf of Mexico.
When the release of built-up forces along a fault creates an earthquake, seismic waves are generated. The seismic waves cause the loose sediments to undulate in wavelike forms, just as the water moves in waves when a pebble is dropped into a lake. If the water table is near the earth’s surface, the undulation creates a mixing action, called liquefaction. Buildings and other hardened structures are often unable to withstand exaggerated earth movements enhanced by soft sediments.
According to an article from ABC News Radio Online (March 2011), a major earthquake along the New Madrid fault line today would be catastrophic, potentially affecting more than 15 million people in eight states: Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri and Tennessee. The USGS reports that the people most at risk from a quake of magnitude 7.0 or 8.0, however, are the approximately one million people living in the Memphis metro area.
The USGS conducted a study in 2009 reporting that a major earthquake along the New Madrid fault line could result in catastrophic loss of life and severe damage to buildings and infrastructure. Unlike California, where building codes include extensive “quake proofing” measures, buildings in cities around the New Madrid have few such requirements.
The Federal Emergency Management Agency (FEMA) also predicts that a major quake at New Madrid could displace 7.2 million people and destroy at least 15 major bridges.
Another problem altogether could result from the 15 nuclear power plants around the New Madrid region. All of the power plants are of the same or similar design as the ones that failed after Japan’s recent earthquake and resulting tsunami, according to ABC News.
The earthquake and resulting tsunami disaster affecting Japan’s Fukushima Nuclear Plan in March 2011 definitely focused attention on the regions of the United States that are vulnerable to earthquakes. The New Madrid region may be particularly unprepared to handle a major earthquake.
And that is
Geography in the NewsTM.
Sources: GITN #153, “Shake, Rattle and Roll,” November 14, 1990; GITN # 1190, “New Madrid Anniversary,” Apr. 22, 2011; http://earthquake.usgs.gov/earthquakes/states/events/1811-1812.php; and http://abcnewsradioonline.com/national-news/potential-catastrophe-earthquake-could-devastate-parts-of-us.html
Co-authors are Neal Lineback, Appalachian State University Professor Emeritus of Geography, and Geographer Mandy Lineback Gritzner. University News Director Jane Nicholson serves as technical editor. Geography in the NewsTM is solely owned and operated by Neal Lineback for the purpose of providing geographic education to readers worldwide.