The increased seismicity is likely due to changes in the way oil and gas are produced. Illustration by Shout

In the fall of 2011, students in Katie Keranen’s seismology course at the University of Oklahoma buried portable seismograph stations around the campus, in anticipation of a football game between the Sooners and the Texas A. & M. Aggies. The plan was to see if the students could, by reading the instruments, detect the rumble of eighty-two thousand fans cheering for a touchdown. “To see if they can figure out if a signal is a passing train or a cheering crowd—that’s much more interesting for them than discussing data in theory,” Keranen, an assistant professor of geophysics, told me.

But at 2:12 A.M. on November 5th, the day of the game, people in seventeen states felt an earthquake of 4.8 magnitude, centered near Prague, Oklahoma, a town of roughly twenty-five hundred, which is about an hour’s drive from Norman, where O.U. is situated. The students quickly packed up the seismographs and headed to Prague, hoping to measure the aftershocks. “Obviously, this was more worthwhile than a game,” Keranen said.

Outside homes around Prague and nearby Meeker, Keranen and her students, along with Austin Holland, the head seismologist of the Oklahoma Geological Survey, buried their equipment. Portable seismographs look like mini-kegs, or time capsules, and they need to be placed underground and on a level. The researchers wanted to install them quickly, since the ground was still shaking.

Shortly before 11 P.M., people in Prague heard what sounded like a jet plane crashing. It was another earthquake, this time a 5.6, followed, two days later, by a 4.7. (The earthquake scale is logarithmic, so a 5.0 earthquake shakes the ground ten times more than a 4.0, and a hundred times more than a 3.0.) No one was killed, but at least sixteen houses were destroyed and a spire on the historic Benedictine Hall at St. Gregory’s University, in nearby Shawnee, collapsed. Very few people had earthquake insurance; the five million dollars needed for the repairs at St. Gregory’s was raised through crowdfunding.

The earthquakes were big news, but the victory of the Sooners—the name comes from the term for those who broke the rules of the 1889 land run and staked claims in advance—was followed more closely. Few noticed that Keranen and her team had gathered likely the best data we have on a new phenomenon in Oklahoma: man-made earthquakes.

At the time, earthquakes were a relatively rare event for Oklahomans. Now they’re reported on daily, like the weather, and generally by the weatherman. Driving outside Oklahoma City one evening last November, I ended up stopped in traffic next to an electronic billboard that displayed, in rotation, an advertisement for one per cent cash back at the Thunderbird Casino, an advertisement for a Cash N Gold pawnshop, a three-day weather forecast, and an announcement of a 3.0 earthquake, in Noble County. Driving by the next evening, I saw that the display was the same, except that the earthquake was a 3.4, near Pawnee.

Until 2008, Oklahoma experienced an average of one to two earthquakes of 3.0 magnitude or greater each year. (Magnitude-3.0 earthquakes tend to be felt, while smaller earthquakes may be noticed only by scientific equipment or by people close to the epicenter.) In 2009, there were twenty. The next year, there were forty-two. In 2014, there were five hundred and eighty-five, nearly triple the rate of California. Including smaller earthquakes in the count, there were more than five thousand. This year, there has been an average of two earthquakes a day of magnitude 3.0 or greater.

William Ellsworth, a research geologist at the United States Geological Survey, told me, “We can say with virtual certainty that the increased seismicity in Oklahoma has to do with recent changes in the way that oil and gas are being produced.” Many of the larger earthquakes are caused by disposal wells, where the billions of barrels of brackish water brought up by drilling for oil and gas are pumped back into the ground. (Hydraulic fracturing, or fracking—in which chemically treated water is injected into the earth to fracture rocks in order to access oil and gas reserves—causes smaller earthquakes, almost always less than 3.0.) Disposal wells trigger earthquakes when they are dug too deep, near or into basement rock, or when the wells impinge on a fault line. Ellsworth said, “Scientifically, it’s really quite clear.”

The first case of earthquakes caused by fluid injection came in the nineteen-sixties. Engineers at the Rocky Mountain Arsenal, a chemical-weapons manufacturing center near Commerce City, Colorado, disposed of waste fluids by injecting them down a twelve-thousand-foot well. More than a thousand earthquakes resulted, several of magnitudes close to 5.0. “Unintentionally, it was a great experiment,” Justin Rubinstein, who researches induced seismicity for the U.S.G.S., told me.

In recent years, other states with oil and gas exploration have also seen an unusual number of earthquakes. State authorities quickly suspected that the earthquakes were linked to disposal wells. In Youngstown, Ohio, in 2011, after dozens of smaller quakes culminated in a 4.0, a nearby disposal well was shut down, and the earthquakes stopped. Around the same time, in Arkansas, a series of earthquakes associated with four disposal wells in the Fayetteville Shale led to a ban on disposal wells near related faults. Earthquakes were also noted in Colorado, Kansas, and Texas. There, too, relevant disposal wells were shut down or the volume of fluid injected was reduced and the earthquakes abated.

But in Oklahoma, which has had more and stronger earthquakes than the other states, it was late 2013 before an owner of a disposal well was asked by the Oklahoma Corporation Commission, which regulates oil and gas exploration, to temporarily reduce its operations—and that was because the well operator himself contacted the O.C.C. and the O.G.S., asking them to look into whether his well was causing problems. So far, there have been only eleven instances in which an owner has, by order, stopped injecting fluids or repositioned a well that was drilled into basement rock.

Driving through Oklahoma’s countryside, you see starlings and cows and nodding donkeys—also known as pumpjacks—and hundreds of disposal wells, of which there are around thirty-two hundred in the state. Disposal wells are generally simple structures: there may be trucks full of water parked nearby, and a typical wellhead is little more than a tank connected to a pump, with some knobs and a few meters visible. “You would be underwhelmed by the technology,” a well-operations engineer told me.

An area of oil and gas exploration is said to be “played out” when it no longer yields sufficient profits, and much of Oklahoma was considered to have been played out in the nineteen-nineties. One problem was the immense quantity of wastewater that was being brought up along with the diminishing yield of oil. “In the past, these wells that brought up so much water were abandoned,” Holland, of the O.G.S., told me. “They didn’t make economic sense. But then a new strategy came along, which was, basically, Let’s just pull up a lot of water.” Dewatering technologies and the rising price of oil made Oklahoma a rich business proposition again.

Although disposal wells have been used for decades, the new dewatering process has led to a dramatic increase in how much water is being disposed of. (In the state, the water used in the initial stage of fracking accounts for less than ten per cent of the water pumped down disposal wells.) In Oklahoma today, an average of about ten barrels of water comes up for every barrel of oil. Holland said, “We’re talking about billions of barrels, and it has to go somewhere.” Todd Halihan, a professor of geology at Oklahoma State University, in Stillwater, told me, “We’re injecting the equivalent of two Lake Hefners”—Oklahoma City’s four-square-mile reservoir—“into the ground each year, and we don’t really understand where that water is going.”