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4/09/2008

Swarm of Small Earthquakes Recorded in Tennessee

Tennessee, USA
In less than 24 hours, a swarm of 28 small earthquakes was recorded near Ridgely, Tennessee, a city 109 miles southeast of Cape Girardeau. Ridgely is at "a junction of two major faults in the New Madrid seismic zone." Multiple earthquakes are common near Ridgely, but are limited to four or five events. Every 20 years or so, a big swarm, such as the one that started Saturday, occurs. It is not clear if the weight of water from recent rains caused the quakes, but scientists are studying the possibilities. "Certainly the occurrence of earthquakes is controlled by the amount of overburden — how much weight is above it." But swarms have occurred in both wet and dry weather. The Ridgely quakes occurred about four miles under the ground's surface. According to the U.S. Geological Survey, the central Mississippi Valley is the most earthquake-prone region of the United States east of the Rocky Mountains. Scientists who follow the small Midwestern quakes linked to the New Madrid fault think in terms of a great quake as a magnitude 8 or greater, which would devastate multiple states. "We have to plan for the worst-case scenarios, but it doesn't do a whole lot of good to scare the public with 8.4 when we're not ready for a magnitude 6." The 28 quakes over the weekend weren't felt by most people.
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