Oklahoma Earthquake Unusual But Not Really Rare

An Oklahoma earthquake racked up a 5.1 magnitude and a whole lot of surprise on Wednesday, but the state is no stranger to tremors.

About 2,000 earthquakes have rattled the state since 1950, including about 200 this year alone, according to data from the Oklahoma Geological Survey.

Wednesday's quake, however, was the second-strongest ever recorded in Oklahoma. Only the April 9, 1952, magnitude 5.5 earthquake registered higher on the Richter scale.

"There's just not that many that have been reported in that range," said Bryan Tapp, chairman of the University of Tulsa's Geosciences Department in the College of Engineering and Natural Sciences.

Between 1950 and 2008 -- the last year complete data were available -- only nine Oklahoma quakes reached a 4.0 or higher, data show. None had an epicenter in Tulsa County.

Like the 1952 earthquake, which was felt in six Midwestern states, Wednesday's quake shook parts of Texas and Kansas, as well. There have even been reports that folks in Kansas City and south of Dallas felt the tremors, Tapp said.

He said it's not uncommon for Oklahoma earthquakes to travel great distances, thanks in part to the old rock that rests under the state.

"You get older and older rocks that have had time to become really quite hard, so the harder the rock, the greater the ability to transmit seismic energy," Tapp said.

But most of the state's earthquakes are weak and felt by few people, if anyone at all.Between 1950 and 2008, the average earthquake registered a 2.0 on the Richter scale, a Tulsa World analysis found.Tulsa County has recorded six quakes in recent decades -- including three in 1983 -- with an average magnitude of 1.5.The strongest to hit the county occurred in November 1983 and measured 2.0 on the Richter scale. Its most recent was a magnitude 1.8 in January 2001.Garvin County has recorded more than 325 earthquakes from 1950 to 2008, the most of any Oklahoma county. Second is Grady County with 214 earthquakes.Diane Noserale, spokeswoman for the U.S. Geological Survey, said that although earthquakes might appear to be increasing, the main reason for the increase is better and more plentiful recording equipment.According to Oklahoma Geological Survey data, 167 earthquakes struck Oklahoma in 1995, the most between 1950 and 2008. Tapp said about 200 have hit the state so far this year."It's not commonly thought of by people, but they do happen in Oklahoma," Noserale said.Tapp said there could be aftershocks to Wednesday's quake, but he doubts that they'd be felt outside the areas near the quake's epicenter around Lake Thunderbird in Norman.
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Source: YellowBrix

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