Days after the largest earthquake in more than four years hit increasingly shaky Oklahoma, environmentalists there are suing three oil companies they say are contributing to the problem.
Saturday's magnitude 5.1 quake was centered in the countryside about 100 miles northwest of Oklahoma City. Hundreds of people in Oklahoma City and in Wichita, Kansas, reported feeling the shake — and so did smaller numbers of people as far away as Dallas and Kansas City, nearly 300 miles from the epicenter.
"Other than the fact that everybody including myself felt more activity, more shaking, more movement than any of the other quakes, amazingly, nobody was injured," said Johnson Bridgwater, director of the Oklahoma chapter of the Sierra Club. "There have been building cracks, foundation cracks, but no serious injuries or anything like that."
The Sierra Club sued Oklahoma-based Devon Energy, New Dominion, and Chesapeake Operating on Tuesday, asking a federal judge to "immediately and substantially" reduce the amount of salty wastewater they're injecting and to reinforce the oil and gas infrastructure scattered around the petroleum-rich state.
Related: [A Series of Strong Quakes in Oklahoma Triggers Republican Scrutiny of Oil Drilling](http://A Series of Strong Quakes in Oklahoma Triggers Republican Scrutiny of Oil Drilling)
(http://A Series of Strong Quakes in Oklahoma Triggers Republican Scrutiny of Oil Drilling)Oklahoma is crisscrossed with almost 15,000 miles of pipelines, Bridgwater said. It's also home to one of the world's largest crude storage facilities, in Cushing — which was rattled by a magnitude 4.5 quake in October.
"None of it was built to any sort of earthquake standard," he said. Those facilities need to be inspected and shored up where needed "to make sure that should we get a 6 or a 7 — which we're very concerned about — that they won't collapse or cause any sort of calamity."
And in court papers, the Sierra Club says at least 10 of its members can testify to "concrete harms" from the quakes, such as cracked walls in their homes. Larger quakes "could injure or kill large numbers of people and cause massive environmental devastation," the lawsuit states.
None of the oil companies named in the case responded to requests for comment.
Scientists say the earthquakes that are rattling northern Oklahoma with increased frequency and strength stem from the injection of oil well wastewater deep underground, where it lubricates long-dormant faults. The thousands of wells that dot the state bring up 10 barrels or more of salt water for every barrel of oil they produce, and that brine is taken to a disposal well and pumped several thousand feet below the surface.
In the last decade, as hydraulic fracturing technology has allowed drillers to reach pockets of oil that were previously inaccessible, the volume of wastewater has skyrocketed — and so has the number of earthquakes. The number of quakes of magnitude 3 or higher went from two or three a year a decade ago to two or three a day now. There have been more than 130 in the first two months of 2016 alone — and since large numbers of smaller quakes raise the odds of a bigger one, the spiraling numbers have raised fears that a quake like Saturday's was in the offing.
The US Geological Survey has blamed wastewater injection for the largest quake in Oklahoma's modern history, a magnitude 5.7 that damaged homes and caused minor injuries in the town of Prague in November 2011. Saturday's quake was the largest since then, and it happened in a spot that has been shaking almost daily since early January.
This M 5.1 in Oklahoma is largest earthquake in the state since the M 5.6 in 2011. (See 2011 —> https://t.co/fJniWwDwyi)
— USGS (@USGS) February 13, 2016
Can't conclude if this specific OK quake caused by human activity.But many quakes in area have been triggered by wastewater fluid injection.
— USGS (@USGS) February 13, 2016
The patch of prairie just west of the small town of Fairview produced numerous 3s and several 4s in the past few weeks. George Choy, a seismologist with the US Geological Survey's National Earthquake Information Center in Colorado, said the agency has ringed the area with new instruments in order to get a better picture of the fault that's producing them.
"There are faults in the area that we've been aware of," Choy said. "But that precise fault, I think we need to locate more accurately to determine whether it's a known fault or a new one."
The Oklahoma Corporation Commission, which regulates the oil industry, has responded to the quakes by telling drillers to reduce the depth of their wells or the volumes they pump underground in hopes of preventing tremors. Their latest directive, issued Tuesday tells operators of more than 245 injections wells in northwest Oklahoma to cut back volumes by more than half a million barrels a day, or about 40 percent of current levels.
But Bridgwater said the burdens on the industry can't trump public safety.
"We want safety to come before the idea of profits," he said.
State regulators don't have the power to force the cuts. But Kim Hatfield, an oil executive who leads the Oklahoma Independent Petroleum Association working group on the quakes, said he expects companies to follow the latest demands — even though it's likely to mean shutting down more wells in a state already hard-hit by the global crash in oil prices.
"If we can't get rid of the water, we can't produce the oil," he said.
Related: Welcome to Quakelahoma
Alternative methods of getting rid of the wastewater have their own risks, including spreading the seismicity problem to new areas, he said. And with an estimated 1.5 billion barrels generated in 2014, even just letting the water evaporate could "significantly change the ecosystem of Oklahoma," Hatfield said.
Hatfield said the latest restrictions were in the works long before Saturday's quake, and weren't a "knee-jerk" response to the weekend tremor.
There aren't many injection wells in the area where Saturday's quake happened, "but they've lit up since late December, and it's been a very active swarm, he said. One theory behind the surge around Fairview was that several wells came back on line at about the same time after an ice storm that knocked out power to the area in late December. But he added, "We really don't understand the mechanism all that well. That's something we're trying to more data on and get a better understanding."
Follow Matt Smith on Twitter: @mattsmithatl