NEW YORK • Oklahoma was rocked on Wednesday night by two of the state's largest earthquakes in recent years, further fuelling scientists' concern that the continued burial of oil and gas wastes in seismically active areas is courting a much more powerful earthquake.
The two quakes, measured at magnitudes 4.7 and 4.8, struck at 11.27pm in rapid succession 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, according to the authorities.
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 Dr Daniel McNamara, a research geophysicist at the National Earthquake Information Centre in Colorado, who has followed the state's quakes.
EXPECT LARGER SHOCK
There's a really strong chance that Oklahoma will receive some strong shaking. I'm surprised (Wednesday's shocks) didn't rupture into a larger event.
DR DANIEL MCNAMARA, a research geophysicist at the National Earthquake Information Centre in Colorado.
Referring to the shocks that occurred on 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 21/2 a day, and that number was 50 per cent 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, Governor 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.
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.
In interviews, Dr 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 on 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 on Wednesday.
But the Edmond fault, about 21km 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. NEW YORK TIMES