Last week, Oklahoma found itself in the news again for a swarm of earthquakes that struck the state Tuesday through Thursday. The largest one, at 4.2 on the Richter scale, was large enough to rattle windows and nerves across Edmond, a large suburb of Oklahoma City.

This wasn’t supposed to happen anymore.

In recent years, Oklahoma has seen a massive uptick in earthquakes, a rise that has been linked to wastewater injection wells used in fracking operations. There are already several class action lawsuits over injuries and damage from earthquakes caused by the oil and gas industry, and experts warn that a large earthquake could rupture the country’s largest oil storage facility in Cushing, Oklahoma.

For years, the state was slow to respond, while Gov. Mary Fallin (R) and others questioned the link to human activity. But by late last year, it was clear that something had to be done. The Oklahoma Corporation Commission, a regulatory agency that oversees injection wells, issued guidance in December to reduce injections. Under that program, operations are paused after a 3.0-magnitude earthquake and halted after a 3.5-magnitude earthquake. The plan seemed to work.

In June, the OCC issued a press release touting the program’s success.

“While still evolving, the ‘traffic light’ protocol system… has thus far yielded some good results,” OCC Oil and Gas Division Director Tim Baker said in a statement. At the time, the OCC had directed wastewater disposal operations to take action after 27 earthquakes of 2.5 magnitude or higher.


Jeremy Boak, director of the Oklahoma Geological Survey, said that “in the cases where companies have taken mitigation actions, the earthquake activity either stopped quickly or tapered off and stopped soon after.”

Then, last Tuesday, there was a 3.0 in Edmond. Then a 3.5. On Wednesday, there was another 3.0, then a 3.3., a 2.6., and the 4.2. (The Richter scale is a base-10 logarithmic scale, meaning a 4.0 is 10 times as large as a 3.0, which is 10 times as large as a 2.0, and so on.) On Thursday, there was another 3.5, a 1.7, and a 3.3. Elsewhere in the state, earthquakes continue to happen most days.

It’s a lot better than it used to be. In 2016, Oklahoma registered 639 earthquakes over a 3.0, and 21 of them were magnitude 4.0 or greater, including the state’s biggest ever, which came in at 5.8 and is now the subject of multiple lawsuits. In the first six months of this year, 137 earthquakes over 3.0 struck, and none of them came in over 4.0. Oil and gas production was not significantly up or down, so the fact that Oklahoma made it through the first half of this year with a mere fraction of its former earthquakes is laudable.

But, as last week showed, it’s not enough.

The OCC plan is definitely helping, but, by nature, it is not going to stop earthquakes, since wastewater injections are only put on hold after an earthquake is triggered. Without stopping wastewater injections, Oklahoma will continue to have earthquakes. Some of them might be large.


“Seismicity lags,” explained Daniel McNamara, a geologist with the U.S. Geological Survey. Injections today could take six months to a year to induce an earthquake. He pointed to one study that came out last year, suggesting that even if injections stopped now, induced earthquakes — that is, earthquakes that are occurring because of human activity — would continue to hit Oklahoma through 2025.

“Even if Oklahoma were to completely shut down fracking, you would see earthquakes for years,” McNamara told ThinkProgress. “The system is so saturated.”

Northeast Oklahoma is susceptible to seismicity. Underground, there are many fault lines, or small cracks in the earth. Unlike the more famous San Andreas fault, which is a long, continuous, surface-level fault, these are smaller and can run in all directions. They can be vertical, like the San Andreas, or horizontal, or placed at any angle in between. Until the fault slips, geologists don’t even know where they might be. Meanwhile, there are thousands of wastewater injection wells.

“You can’t really link one well to one earthquake,” McNamara said.

The faults are continuously under two kinds of pressure: “normal stress,” which holds them in place, and “sheer stress,” which tries to make them shift. The most common way wastewater triggers earthquakes is by reducing the normal stress. When wastewater is injected underground — deeper than fracking usually happens, and much deeper than surface or groundwater reserves — it is injected right into the rock. The rock is porous and permeable, meaning it has lots of little holes, and water can pass from hole to hole. It’s sponge-like, but there’s a key difference: while a sponge soaks up water, rock must be injected with water. Once that happens, the water starts to spread out in a wave of pressure, like the ripple from a pebble dropped into a still lake. When that pressure hits a fault line, it can reduce the normal stress. The earth slips, causing an earthquake.


“The issue occurs when you have wastewater injection that is near existing faults. There are other ways, but this is the most common,” said Noel Bartlow, an assistant professor at the University of Missouri. “People should not inject next to known faults.”

Even when wastewater is injected near a fault line, it might not cause anything to happen. The normal stress might be too high or the water pressure too low.

Lags occur in lots of different ways. The water could take a while to reach a fault line, for instance, or it could loosen the fault so that a natural shift tips it over the edge. “We know a lot more than we knew just a couple years ago,” Bartlow said. But, he added, “there’s a lot we don’t know or we would like to know.”

It’s not clear exactly what happened with last week’s earthquakes in Oklahoma.

When a swarm of EQ occurs, they are typically related to each other, Bartlow said. They could be happening on the same fault. They could be happening on connected faults. The same wastewater fluid could seep outward and hit multiple faults around the same time. Or an earthquake could “perturb forces” in the area, triggering other earthquakes.

In the 1970s, Denver was hit with a spate of induced earthquakes. The state shut down wastewater disposal, and the USGS took the opportunity to drill some wells and do some targeted testing. In that case, they found that the pressure and volumes of injection could be linked to the magnitude of the induced earthquake.

And Oklahoma’s regulatory system is just catching up. Until a massive uptick in earthquakes in 2010 attracted the attention of Oklahoma residents, the USGS, the OCC, and news media around the country, wastewater disposal operations were only required to report their total annual wastewater volumes. Now, the OCC demands monthly reports showing weekly volume data, but the lack of oversight muddies the water for geologist trying to map out where the faults are and how they might be connected.

That job falls to the USGS, but “it’s hard to do detailed studies,” McNamara admits.

Last year, the regional EPA office sent the OCC’s top brass — including the chair, vice chair, and a commissioner — a letter urging the commission to take greater steps to reduce wastewater injections. A couple weeks later, the OCC issued the new directive, which a spokesperson for the agency said had already been in the works. In the letter, the EPA warned that a 5.0 earthquake near Cushing, about 60 miles from Edmond, “raises concern over risks to public safety and the environment.”

“The U.S. Department of Homeland Security (DHS) projects that a quake of magnitude 5.7 could significantly damage the oil storage tanks in Cushing,” the letter stated. “As you fully recognize, a breach in the integrity of the Cushing pipelines and storage facilities could be catastrophic for both the environment and the national energy system given the more than 80 million barrels of crude oil storage capacity.”

“The work to ensure the safe, responsible, and economically viable development of Oklahoma’s oil and gas resources is an ongoing process,” state seismologist Jacob Walter said in the June statement. “When it comes to all forms of induced seismicity we know far more now than we did only a few years ago, but there’s much work that remains. [Oklahoma Geological Survey] will continue to monitor and track seismic activity and lead research projects to better understand induced seismicity.”

In a state where the governor urged residents to “pray for oil” a few years ago, where the state house was built within site of drilling rigs, and where the biggest political players on the scene are all connected to fossil fuels, it’s hard to imagine that Oklahoma will be taking drastic measures.

In the meantime, McNamara recommends people in Oklahoma start thinking like Californians, securing knickknacks on their shelves and learning about earthquake preparedness.

“They are now living in active earthquake country,” he said.