for National Geographic News
The strongest earthquake to hit the Gulf of Mexico in 33 years shook the southern United States Sunday, prompting thousands of calls to authorities.
The magnitude 6.0 temblor, centered about 330 miles (530 kilometers) southeast of New Orleans, Louisiana, occurred at 8:56 a.m. local time (map of Louisiana). It was felt in parts of Florida, Georgia, Alabama, Louisiana, and Mississippi.
Damage, if any, was too light to be reported. The earthquake was also too weak to cause a tsunami.
And Sunday's quake should have little to no effect on development of recently discovered oil reserves deep beneath the Gulf, says Randy Cox, an associate professor of earth science at the University of Memphis in Tennessee.
Powerful earthquakes are rare but not unheard of in the Southeast U.S.
In 1879 an earthquake near St. Augustine, Florida, rattled dishes off shelves and cracked plaster. And in 1886 a magnitude 7.3 temblor killed 60 people in Charleston, South Carolina, and rang church bells as far away as St. Augustine.
Most earthquakes take place near the edges of the tectonic plates that make up Earth's crust. Stress builds as the plates slowly but steadily collide.
The mammoth tsunami-generating quake in Indonesia on December 26, 2004, occurred at such a plate boundary.
The recent Gulf of Mexico earthquake, however, occurred in the middle of a plate, not at an edge.
Such "mid-plate" earthquakes probably represent release of long-term stress originating from distant forces, the U.S. Geological Survey says on its Earthquake Hazards Program Web site, which tracks earthquakes around the globe.
The earthquake occurred along a region known as the Cuba fracture zone, Cox says.
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