Oklahoma was rocked Wednesday night by two of the state's largest earthquakes in recent years, further fueling scientists' concern that the continued burial of oil and gas wastes in seismically active areas was courting a much more powerful earthquake.
The two quakes, measured at magnitudes 4.7 and 4.8, struck at 11:27 p.m. in rural northern Oklahoma, directly beneath a major oil and gas production area. The second quake, which came about 30 seconds later, was the fourth-largest recorded in the state. There were no reports of injuries or damage, the authorities said Thursday.
The two quakes followed a series of smaller ones last week that peeled brick facades, toppled columns and caused a power failure in Edmond, an upscale Oklahoma City suburb. Some experts said those quakes hinted at the possibility of a larger shock.
"I do think there's a really strong chance that Oklahoma will receive some strong shaking," said Daniel McNamara, a research geophysicist at the National Earthquake Information Center in Colorado, who has followed the state's quakes.
Referring to the shocks that occurred Wednesday night, he added, "I'm surprised it didn't rupture into a larger event."
Five years ago, Oklahoma recorded three earthquakes of magnitude 3 — roughly the level at which shocks are felt — or greater. Last year, it recorded 907 quakes, or nearly 2 1/2 a day — and that number was 50 percent higher than in 2014.
Virtually all the quakes are the result of slippage in faults that have effectively been lubricated by watery wastes from oil and gas production that have been pumped underground.
In a state where oil and gas carry immense economic and political clout, Gov. Mary Fallin and the state Legislature have left it to the Oklahoma Corporation Commission, which oversees the industry, to find a solution.
With no explicit authority to regulate seismic issues, the commission has persuaded producers to voluntarily follow a series of ever-stricter directives on waste disposal in earthquake zones. But while those orders appear to have curtailed earthquakes in some areas, the overall number has continued to soar.
Last month, a financially troubled producer in the northern oil and gas fields struck by Wednesday's quakes, SandRidge Energy Inc., broke industry ranks and refused the commission's request to scale back its underground waste disposal. The two sides are scheduled to meet Friday in a final attempt to avert a court battle over the commission's authority.
Some critics charge that the state and the commission are moving too slowly and deferring too often to industry leaders, and that more sweeping action is needed.
Cory Williams, a Democratic state representative who has called for action on the issue, said it was unlikely that the Legislature, which is scheduled to meet this month, would act.
"Absent a catastrophic loss of life or property, there will be zero reaction from the Oklahoma House or Senate," he said in an interview. "They don't want to touch it. It's a third rail."
But Oklahoma's secretary of energy and environment, Michael Teague, said in an interview that regulators had sufficient power to rein in waste disposal and the full support of Fallin, a Republican.
"I don't think we need legislative action," he said. "We all know this is a problem we have to solve."
The president of the Oklahoma Oil and Gas Association, Chad Warmington, said he believed that the regulators' "measured" steps to rein in waste disposal in quake zones were working, but that there might be a lag between the cutbacks and a decrease in tremors.
In interviews, McNamara and two other scientists who have studied earthquakes in the state stressed that it was impossible to say with certainty whether larger shocks would follow. They added, however, that science and statistics suggest that the possibility is rising.
Both quakes Wednesday, and the earlier ones in Edmond, occurred in faults running northeast-to-southwest that are the most prone to slipping. A similar fault near waste-disposal wells produced a magnitude-5.7 earthquake in 2011 that was the largest in Oklahoma history.
Experts still do not know the size of the northern Oklahoma fault involved in the tremor Wednesday. But the Edmond fault, about 13 miles long, is capable of producing a shock as big as the record 2011 one, they said.
That quake damaged dozens of homes in rural Prague, but the effect in a heavily populated area would be much greater, they said.