Third Earthquake Recorded In Southeastern Oklahoma

February 4, 2009

For the third time in less than a week a small earthquake has been recorded in Oklahoma, but geological experts say these occurrences are not uncommon or cause for alarm.

The U.S. Geological Survey reported a magnitude 3.2 earthquake occurred at 5:23 a.m. Tuesday about 25 miles east of Ada, with the epicenter about two miles northwest of the junction of State Highway 3 and U.S. 75.

Last Thursday a 2.4 magnitude quake was recorded about 7 miles northwest of Chandler in Lincoln County, and last Wednesday a 3.4 magnitude quake was recorded about 5 miles northeast of Chickasha.

“We have about 50 earthquakes a year, so it’s not that unusual in terms of frequency,” said Kenneth Luza, an engineering geologist at the Oklahoma Geological Survey in Norman. “It might be a little more unusual that we had so many felt earthquakes.”

A magnitude 2.5 to 3 quake is generally the smallest that is felt by people, but Luza said people have reported feeling earthquakes as small as a 1.4.

“If the atmospheric conditions are right, there’s no wind and it’s very quiet … you could feel that,” he said.

The quakes in Oklahoma generally last only a few seconds and occur about 3 to 5 miles below the surface when opposing fractions of the earth’s crust move slightly, releasing energy that causes a small quake, Luza said.

“As the strain builds up along this fault zone, it pops or moves,” he said. “We’re talking millimeters, fractions of an inch that you don’t see at the surface.”

Luza said Oklahoma has three main areas where earthquakes occur: the most active is a central Oklahoma fault zone roughly between Norman and Pauls Valley, the second is in the Arkoma basin region in southeastern Oklahoma, and the third is in the Canadian County area.

This third region is where the state’s largest ever recorded earthquake took place _ a magnitude 5.5 earthquake centered in El Reno in 1952 that toppled chimneys, cracked foundations, loosened bricks and broke windows and dishes, according to a USGS report.

Luza said one woman was injured at a Tulsa bank when a ceiling tile fell and hit her in the head, and the quake produced a crack at the state Capitol that measured 15 meters long. He said the quake could be felt as far away as Des Moines, Iowa, and Austin, Texas.

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