Oklahoma Earthquake Felt in Several U.S. States, as Oil Wells Draw Scrutiny

A 5.6-magnitude earthquake rattled Oklahoma on Saturday, damaging buildings and tying for the strongest temblor ever recorded in the state, which has experienced a rash of earthquake activity in the past decade that U.S. seismologists have tied to the underground disposal of wastewater from oil and gas drilling.

Oklahoma Gov. Mary Fallin said via Twitter on Saturday afternoon that state regulators were contacting operators of about 35 disposal wells in a 500-square-mile area and asking them to shut down following the quake.

The earthquake took place around 7:02 a.m. central time near Pawnee, Okla., a town of about 2,200 people roughly 55 miles northwest of Tulsa, according to the U.S. Geological Survey. It was felt widely through the middle of the country, with reports coming from as far as Houston and Kansas City, according to the USGS.

There were no immediate reports of injuries, but local television reports showed damage to some buildings in Pawnee. It wasn’t clear whether the temblor was natural or triggered in part by human activity.

An assessment deemed six buildings in the Pawnee Nation reservation uninhabitable, Gov. Fallin wrote on Twitter. In rural Pawnee County, three homes were damaged and a homeowner was taken to the hospital after suffering minor injuries in the quake, she wrote.

Staff from the Oklahoma Department of Emergency Management were in Pawnee assessing damage to buildings, said Keli Cain, spokeswoman for the department.

Residents in Oklahoma City and Stillwater, a city southwest of Pawnee that is home to Oklahoma State University, have also reported building damage via social media, Ms. Cain said.

“We’re monitoring social media, and we’ve seen some reports,” she said. The department hadn’t received reports of serious injuries.

Chunks of a 100-year-old building fell two stories to litter the sidewalk near the Pawnee’s main street, officials said.
Kyndra Richards cleans up spilled boxes at “White’s Foodliner” store after an early morning earthquake in Pawnee, Okla., on Saturday. ENLARGE
Kyndra Richards cleans up spilled boxes at “White’s Foodliner” store after an early morning earthquake in Pawnee, Okla., on Saturday. Photo: Associated Press

“That’s one of our historic buildings,” said Lou Brock, a city councilman.

Mr. Brock said he was awake and was wishing a friend happy birthday when the rumbling started. “This was not the gift I wanted to give them,” he said. He felt the ground moving for over a minute.

“One of those incredible feelings,” he said.

The city asked residents to report any structural problems or smells of gas, he said.

“Right now the situation is that as long as we get the most information from our wonderful city people I think we’re going to be just fine,” Mr. Brock said.

Gov. Fallin, a Republican, said in a Twitter post that structural engineers found very minor issues and none concerning structural problems with state highway and Oklahoma Turnpike Authority bridges following the quake. Oklahoma Corporation Commission staffers were also reviewing oil and gas wastewater disposal wells in a 725-square-meter “area of interest” around the quake area, she added.

So far, the commission has ordered at least 37 wells to be shut down within a week to 10 days. “This is a mandatory directive,” she wrote, adding that state regulators are working with the Environmental Protection Agency in Osage County. The governor didn’t say why the state ordered the wells to close.

Representatives for the governor and the Oklahoma Corporation Commission didn’t immediately respond to requests for comment.
Earthquake Risk Higher in Energy-Intensive States: USGS
0:00 / 0:00

Oklahoma has a history of seismic activity, and earthquakes in the state aren’t unheard of. But it has stepped up regulation of the wastewater injection wells after seeing a dramatic increase in seismic activity over the past decade. In 2015 the USGS recorded 2,500 quakes with a magnitude of 2.5 or higher in the state, up from just three in 2005.

The USGS in March released maps that for the first time show the potential risk of man-made as well as naturally occurring earthquakes, and they listed some parts of Texas and Oklahoma now at the same danger of temblors as California, due largely to the injection-well trend.

The strongest quake previously recorded in Oklahoma was also a 5.6 magnitude event, and took place near Prague, Okla. in 2011, buckling roads and destroying 14 homes. It spurred several lawsuits from homeowners who claimed energy companies burying wastewater nearby had helped trigger the quake.

When energy producers extract oil and gas from wells, thousands of barrels of salty water laced with heavy metals come up along with the fuel. The water often is injected back underground under high pressure into special disposal wells.

But government and academic researchers have found that the practice may help trigger movement along geologic fault lines. The oil-and-gas industry has acknowledged the validity of the studies and cooperated with regulators, but has said that more research is needed to link specific wells to specific incidents.

After Oklahoma’s Corporation Commission began taking stronger actions to police the location and volume of injection wells, the number of quakes in the state fell by roughly 25% compared with a year earlier, state officials said in June.

The Cooper Nuclear Station near Brownville, Neb., experienced minor tremors from the earthquake and declared an “unusual event” at 7:10 a.m., according to a press release. There is no threat to the public or plant personnel, and the station continues to operate safely, the release said.

The quake’s epicenter was roughly 25 miles north of Cushing, Okla., one of the world’s major oil hubs. The town holds some 64 million barrels of crude in about 400 massive, aboveground tanks.
The side of the historic Pawnee County Bank was missing sandstone bricks following Saturday’s earthquake in Pawnee, Okla. ENLARGE
The side of the historic Pawnee County Bank was missing sandstone bricks following Saturday’s earthquake in Pawnee, Okla. Photo: Associated Press

A representative of Enbridge Inc., one of the top pipeline and storage companies in Cushing, said no damage had been reported at its sites there.

“Following the earthquake, Enbridge employees were directed to conduct visual inspections of tanks, manifolds and other facilities. The Cushing Terminal is currently operating normally,” the company said.

Bruce Heine, a spokesman for Magellan Midstream Partners LP, which is another tank farm owner in Cushing, said in an email, “We have no damage to report at this time.”

The quake was the largest one in the continental U.S. this year, according to Lucy Jones, a quake expert and seismologist formerly with the U.S. Geological Survey. Only Alaska has had a larger quake this year, she said in a flurry of Twitter responses she typically unleashes after a significant quake.

Scientists have linked the increase in the rate of quakes in the region of Saturday’s temblor to the rise of the oil and gas industry, especially the injection of wastewater into the ground. But it is more difficult to link specific quakes to those processes.

Some scientists have suggested man-made quakes can’t produce shaking as intense as naturally occurring quakes, possibly because the faults haven’t reached maximum stress levels before the injections weaken them and cause a break.

Dr. Jones said Oklahoma’s longest fault is long enough to produce a magnitude 7 quake.

—Dan Molinski and Tammy Audi contributed to this article.

Write to Miguel Bustillo at miguel.bustillo@wsj.com