Minor Earthquake on New Madrid Fault
Feb. 22, 2012
A minor earthquake struck the New Madrid Seismic Zone (NMSZ) in the central United States only days after the 200th anniversary of the last of three massive quakes that rocked that area in the early 1800′s. People in at least nine states felt the 4.0-magnitude quake, which struck at 3:28 a.m. (Eastern Standard Time) on Feb. 21, 2012. Only minor damage was reported. The quake’s epicenter was located near East Prairie, Missouri, about halfway between St. Louis and Memphis.
A seismic zone is an area on the surface that is or could be affected by shifts in interconnected faults (fractures) in Earth’s lithosphere (crust and upper portion of the mantle). The NMSZ is an area of high earthquake activity that is centered in the Boot Heel region of southeastern Missouri and includes parts of northeastern Arkansas, southern Illinois, and western Kentucky. More earthquakes occur in this region than in any other area of the United States east of the Rocky Mountains.
The New Madrid earthquakes were the largest quakes to strike the United States since the arrival of European settlers in North America. The quakes, all of which had an estimated moment magnitude of at least 7.5, affected an area about 10 times as large as that affected by the stronger San Francisco earthquake of 1906 and Haiti earthquake of 2010. The first quake, which took place on Dec. 16, 1811, was widely felt across the Eastern United States. The shaking woke people in New York City and Washington, D.C., and rang bells in Boston. The second quake occurred on Jan. 23, 1812. The third quake, which may have been the most violent of the three, destroyed the town of New Madrid, Missouri, and damaged many buildings in St. Louis. Large waves called seiches swept northward in the Mississippi River, giving the impression that the river was flowing backwards. The death toll from the New Madrid quakes is unknown. However, if any deaths occurred, the number was probably very small. The population of the area at that time included only about 100,000 non-Indians and a somewhat greater number of Indians. St. Louis had an estimated population of 5,700 in 1811. A major earthquake along the New Madrid fault today could affect about 40 million people, 12 million of whom live in the NMSZ itself.
The NMSZ remains an area of high earthquake activity. According to the United States Geological Survey (USGS), large earthquakes in this zone could be more devastating than those in California for a number of reasons. Because of the nature of the crust in the Midwestern United States, shaking from an earthquake would travel farther. The region also has many buildings that have not been built or reinforced to limit earthquake damage. In addition, most people in the region are unprepared to cope with a major earthquake. A recent study estimated that a magnitude-7.7 quake along the New Madrid fault would cause 3,500 deaths and 80,000 injuries as well as the displacement of at least 2 million people in the NMSZ alone. The USGS has estimated that there is a 7 to 10 percent chance that a major NMSZ earthquake (magnitude 7.5 to 8.0) could occur within the next 50 years.
Additional World Book articles:
- Geology
- Plate tectonics
- Richter magnitude
- San Andreas Fault
- When the Earth Moves (a Special Report)