Oklahoma earthquake felt as far away as Arizona
Temblor shakes up Midwest and the debate on underground disposals.
OKLAHOMA CITY— A record-tying earthquake at the edge of Oklahoma’s key energy-producing areas rattled the Midwest from Nebraska to North Texas on Saturday and likely will bring fresh attention to the practice of disposing oil and gas field wastewater deep underground.
The United States Geological Survey said a 5.6 magnitude earthquake happened at 7:02 a.m. local time Saturday in northcentral 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 waste water-well owners to reduce disposal volumes in parts of the state, directed 37 wells within an approximately 500-squaremile area around the epicenter to shut down within seven to 10 days because of previous links between the injection of wastewater and quakes.
“All of our actions have been based on the link that researchers have drawn between the Arbuckle disposal well operations and earthquakes in Oklahoma,” spokesman Matt Skinner said Saturday. “We’re trying to do this as quickly as possible, but we have to follow the recommendations of the seismologists, who tell us everything going off at once can cause an (earthquake).”
People in St. Louis and Kansas City, Mo.; Chicago;
Gilbert, Ariz.; Fayetteville and Little Rock, Ark.; Des Moines, Iowa; Memphis, Tenn.; and Big Lake in southwest Texas all reported feeling the quake.
Pawnee County, Okla., Emergency Management Director Mark Randell said no buildings collapsed in Pawnee, a town of 2,200 about 9 miles southeast of the epicenter.
“We’ve got buildings cracked,” Randell said.
The damage is not as severe as the 2011 quake near Prague, about 60miles south of Pawnee, despite being the same magnitude and about the same depth below the surface. Saturday’s was 3.7 miles deep, compared to 3.1 miles in 2011. Both were shallow quakes, during which shaking is more intense, like setting off “a bomb directly under a city,” USGS seismologist Susan Houghsaid.
However, hard bedrock beneath the surface in north-central Oklahoma is likely the reason for the lesser damage, Oklahoma Geological Survey geophysicist Jefferson Chang said, adding that the subsurface around Prague is softer.
“In harder rock, it won’t shake as much,” Chang said.
Pawnee furniture store owner Lee Wills said at first he thought it was a thunderstorm.
“Everything went crazy
after that. It just started shaking,” said Wills, who lives about 21⁄ miles outside 2 of town. “It rocked my house like a rubber band.”
The office of Oklahoma Gov. Mary Fallin tweeted that state highway crews were checking for bridge damage and that the state Department of Emergency Management would assess damage.
Some parts of Oklahoma now match northern California for the nation’s most shake-prone, and one Oklahoma region has a 1 in 8 chance of a damaging quake in 2016, with other parts closer to 1 in 20.
The area where the quake was centered is on the edge of a region covered by a “regional earthquake response plan” issued in March by the Corporation Commission, whose goal was to cut the number of earthquakes by reducing wastewater injection volume by 40 percent from 2014 levels.
Oklahoma was late in imposing volume limits, taking a different approach to Kansas after both states had an uptick in quakes in the first half of this decade. Kansas moved quickly to limit volume while Oklahoma concentrated on the depth of the disposal. Kansas saw a 60 percent drop while the frequency of quakes in Oklahoma continued to climb.