Oklahoma Just Had Its Biggest Quake Ever, and There May Be More to Come

Oklahoma’s recent string of earthquakes are something new for the state

The magnitude 5.8 earthquake that struck Pawnee, Oklahoma, on Sept. 3 is officially the state's largest on record. Geologists believe that activities related to oil and gas extraction in the state have triggered a quake swarm in the seismically active region. Public Domain

When a magnitude 5.5 earthquake roiled El Reno, Oklahoma, on April 9, 1952, workers paused in shock to see their cash registers jittering, desks quivering and typewriters swaying. Then they evacuated in a state of panic. Though only one person was injured in the temblor, the event was rare and troubling.

But when an earthquake that clocked in at magnitude 5.8 roiled Oklahoma on Sept. 3, sending tremors to neighboring states and cracking old buildings near its epicenter, it came as no surprise. These days, earthquakes are a routine part of life in the seismically active state. Since 2009, it’s become an unlikely earthquake hotspot, experiencing more magnitude 3.0 and higher quakes than California in both 2014 and 2015. But why?

Jeremy Boak, who directs the Oklahoma Geological Survey, thinks he has the answer—oil and gas extraction in the state. The phenomenon is called “induced seismicity,” and it’s become a buzzword in a state that depends on oil and gas for much of its revenue (approximately one in four Oklahomans works in oil and gas.) But oil extraction in the state leads to something else: wastewater that is disposed of deep in the ground and may be the source of the recent quake swarm.

Oklahoma has always been seismically active. The OGS has recorded quakes since 1882, but they definitely weren't the region's first. Boak explains that a paleoearthquake of at least a magnitude 7 is thought to have occurred about 1,300 years ago—one of many in the region, which lies in the New Madrid Fault Zone. It's the eastern United States' most active seismic area, but unlike faults like, say, the San Andreas Fault, the faults are tucked beneath hundreds of feet of soft layers of river soils. Bigger quakes can shake the New Madrid, as in 1811 when a Missouri quake set off mass chaos in the area. But the 1952 quake was one of just a few larger temblors. In fact, by 1962, only 59 Oklahoma earthquakes total had ever been recorded.

Now, however, the story is different. As Oklahoman oil production has risen, so have the number of earthquakes. Around 2009, Boak tells Smithsonian.com, “most faults in the central part of the U.S. were very close to critical stress. They were kind of ready to go.”

Though the word “fracking” might cross your mind when you hear about human-induced quakes, the practice doesn’t seem to be linked to the majority of the manmade quakes in Oklahoma. Hydraulic fracturing pumps a controversial cocktail of water and chemicals into geologic formations to crack the shale rock deep inside the earth, yielding more oil and gas. But the Oklahoma Geological Survey ties most of the manmade quakes in the state to wastewater disposal wells. Those wells, filled with pressurized byproducts of oil extraction, can set off an earthquake.

Humans have been accidentally triggering quakes for decades. As the U.S. Department of Energy explains, oil production in California in the 1930s induced a series of earthquakes due to a kind of geologic collapse triggered by removing too much oil without balancing the pressure out with water. Modern water injection has a different purpose—to get rid of the millions of gallons of saltwater that gush up to the surface along with oil and gas. The water is not only useless because of its high salt content, it’s also expensive to get rid of. So oil producers simply inject it back into the earth again.

That might not be an issue with small-scale oil production, but we’re talking a lot of water. “Ten, 20, I’ve even heard 50 barrels of water per barrel of oil,” says Boak. And then there’s Oklahoma’s unique geologic landscape. “In certain formations you can put it back down underground and use it to drive more oil into your producing wells, but [Oklahoma’s] wells are already wet,” Boak explains.

So the water is injected into a deep zone known as the Arbuckle formation, which has become a kind of underground disposal area for the oil and gas industry. This layer of rock—Oklahoma’s deepest sedimentary layer—is beneath the area where oil and gas is extracted, so it has not been studied as much. What is known is that the porous rock takes up lots of water and has kept accepting water over the last half-century, so it’s become the layer of choice for oil companies with water to get rid of.

Despite mounting evidence that wastewater disposal linked to oil and gas is causing the quakes, scientists still aren’t exactly sure what happens to the water once it gets into the Arbuckle. Does it drain into the basement rock beneath? Does something else happen to it? Do the faults causing the earthquakes even extend all the way down into the Arbuckle? It simply isn’t clear, says Boak.

 “We have no proof that there is a communication pathway down,” he admits. But something seems to be happening in the Arbuckle—and Boak’s organization currently thinks that faults are slowly pressurized with water, then spurred to seismic activity when pressure rises above a certain level.

That pressure has translated into a veritable pressure cooker for Oklahoma residents, who have experienced property damage and the unsteady feeling of seemingly constant earthquakes since the seismic surge. Insurance rates have risen 300 percent or more since 2009. About 20 percent of Oklahomans now have earthquake insurance, but given that such insurance usually only covers catastrophic damage, it’s not much of a comfort.

For Angela Spotts, enough was finally enough on October 10, 2015, when a 4.5 magnitude earthquake struck about 20 miles away from her home in Stillwater. “October 10 was truly a defining moment,” she tells Smithsonian.com. “[My husband and I] both looked at each other and went ‘wow, I don’t want to live like this anymore.’” Spotts, who spent years fighting both wastewater disposal and fracking in Oklahoma, says that the stress from ongoing quakes was a major factor in her decision to move to Colorado, where she now owns and operates a small hotel. She accuses the state of colluding with the oil and gas industry and dragging their feet on helping real Oklahomans deal with the new instability of the earth below.

After years of inaction, Oklahoma is finally cracking down manmade quakes. The state’s oil and gas regulator, the Oklahoma Corporation Commission, avoided action on Arbuckle wells for years. But recently, it’s shown signs of finally taking the quake problem seriously—largely after earthquakes rattled the homes of elected officials. The Commission has released several response plans, has adopted a “traffic light” system for permitting disposal wells, adopted stricter monitoring and reporting rules and regulated how deep water can be injected. It took years of lawsuits and community organizing by people like Spotts to get the issue on the legislative radar.

Chad Warmington, president of the Oklahoma Oil & Gas Association, tells Smithsonian.com that the oil and gas industry is working closely with regulators and geologists to help prevent manmade quakes. “I’m pretty pleased with the outcome,” he says. “We’ve made a very honest effort to really figure out what is going on and what we can do to impact the seismicity outbreak in the state.” He says that association members have borne the brunt of the regulatory cleanup, providing proprietary data to geologists and cutting back production. Indeed, some producers like SandRidge Energy, which fought hard against the restrictions, have since declared bankruptcy.

“The restrictions have done exactly what they wanted them to do,” said Warmington. “It’s reduced earthquakes, it’s reduced production and it’s driven the oil and gas industry elsewhere.”

While Boak says that earthquakes have dropped off since 2014, when the strictest regulations were introduced, he notes that much of the reduction was likely driven by declines in oil prices. But both agree that if oil prices rise again, producers will still be forced to dispose of less water, which will likely affect future quakes.

For Spotts, that simply isn’t good enough. “Why should one group of people have to take it just because we live in the wrong place?” she says. “It’s manmade and they’re taking advantage of us.”

“The water has to go somewhere,” counters Warmington. “Until they come up with a way to dispose of it that’s cheaper, it’s going to be a severely limiting factor.”

After last weekend’s quake, 37 wells remain shut down by the state as a precautionary measure. But will the problem simply drift to another state as Oklahoma gets tougher on oil and gas wastewater disposal? We may soon find out: The U.S. Geological Survey has tied spikes in earthquakes in states like Kansas, Ohio, Texas and Arkansas to the practice and says that some seven million people live in a place that could experience a damaging, manmade earthquake this year. Unlike Oklahoma, Kansas has limited how much wastewater may be injected as opposed to how deep it may go. To truly cut the number of earthquakes created by humans, the answer may not lie in how much water is disposed of, but whether water is disposed of at all.

Get the latest Science stories in your inbox.