Record-tying Oklahoma earthquake felt as far away as Illinois

OKLAHOMA CITY -- A record-tying earthquake in the edge of Oklahoma's key energy-producing areas rattled the Midwest from Illinois to the southwest part of Texas on Saturday and likely will bring fresh attention to the practice of disposing oil and gas field wastewater underground.

The United States Geological Survey said a 5.6-magnitude earthquake happened at 7:02 a.m. Saturday in north-central Oklahoma, on the fringe of an area where regulators had stepped in to limit wastewater disposal. That temblor matches a November 2011 quake in the same region.

An increase in magnitude-3.0 or greater earthquakes in Oklahoma has been linked to underground disposal of wastewater from oil and natural gas production.

The Oklahoma Corporation Commission, which since 2013 has asked wastewater-well owners to reduce disposal volumes in parts of the state, is requiring 37 wells in a 514-square-mile area around the epicenter of the earthquake to shut down within seven to 10 days because of previous connections between the injection of wastewater and earthquakes.

People in Kansas City and St. Louis; Chicago; Gilbert, Arizona; Fayetteville and Little Rock, Arkansas; Des Moines, Iowa; Memphis, Tennessee; and Big Lake in southwest Texas, all reported feeling the earthquake. Dallas TV station WFAA tweeted the quake shook its studios, too.

Pawnee County Emergency Management director Mark Randell said no buildings collapsed.

"We've got buildings cracked," Randell said. "Most of it's brick and mortar, old buildings from the early 1900s."

Randell also said a man suffered a minor head injury when part of a fireplace fell on him as he protected a child. The man was treated and released.

Oklahoma Gov. Mary Fallin has declared a state of emergency for the county, allowing state agencies to make emergency purchases related to disaster relief and preparedness. The declaration is also the first step toward seeking federal aid should it be necessary

The damage is not as severe as the 2011 quake near Prague, Oklahoma, about 60 miles south of Pawnee, despite being the same magnitude and approximately the same depth. Saturday's was 3.7 miles deep, compared to 3.1 miles in 2011. Both are shallow quakes, during which shaking is more intense, like setting off "a bomb directly under a city," USGS seismologist Susan Hough has said.

However, hard bedrock beneath the surface in north-central Oklahoma is likely the reason for less damage, Oklahoma Geological Survey geophysicist Jefferson Chang said, adding the subsurface around Prague is softer.

"It's pretty much comparable to the Prague event," Chang said. "But in harder rock, it won't shake as much."

Pawnee furniture store owner Lee Wills said he first thought it was a thunderstorm.

"Then it just ... everything went crazy after that. It just started shaking," said Wills, who lives about 2 1/2 miles outside of town. "It rocked my house like a rubber band. Threw stuff off cabinets and out of cabinets, broke glasses."