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At exactly 10:53 p.m. on Saturday, November 5, 2011, Joe and Mary Reneau were in the bedroom of their whitewashed and brick-trimmed home, a two-story rambler Mary’s dad custom-built 43 years ago. Their property encompasses 440 acres of rolling grasslands in Prague, Oklahoma (population 2,400), located 50 miles east of Oklahoma City. When I arrive at their ranch almost a year later on a bright fall morning, Joe is wearing a short-sleeve shirt and jeans held up by navy blue suspenders, and is wedged into a metal chair on his front stoop sipping black coffee from a heavy mug. His German shepherd, Shotzie, is curled at his feet. Joe greets me with a crushing handshake-he is 200 pounds, silver-haired and 6 feet tall, with thick forearms and meaty hands-and invites me inside. He served in Vietnam, did two tours totaling nine years with the Defense Intelligence Agency, and then, in 1984, retired a lieutenant colonel from the US Army to sell real estate and raise cattle. Today, the livestock are gone and Joe calls himself “semiretired” because “we still cut hay in the summers.”

The earthquake registered a magnitude 5.7*-the largest ever recorded in Oklahoma-with its epicenter less than two miles from the Reneaus’ house, which took six months to rebuild. It injured two people, destroyed 14 homes, toppled headstones, closed schools, and was felt in 17 states. It was preceded by a 4.7 foreshock the morning prior and followed by a 4.7 aftershock.

The quake baffled seismologists. The only possible culprit was the Wilzetta Fault, a 320-million-year-old rift lurking between Prague and nearby Meeker. “But the Wilzetta was a dead fault that nobody ever worried about,” says Katie Keranen, an assistant professor of geophysics at the University of Oklahoma. We’re driving in her red SUV, just south of the Reneaus’ property, when she stops to point out where the quake tore open a footwide fissure across State Highway 62. The United States Geological Survey (USGS) maintains a database of seismically risky areas. Its assessment of the Wilzetta Fault, Keranen notes, was “zero probability of expected ground motion. This fault is like an extinct volcano. It should never have been active.”

When the Wilzetta mysteriously and violently awakened, Keranen wanted to know why. So she partnered with scientists from the USGS and Columbia University’s Lamont-Doherty Earth Observatory. The morning after the initial foreshock, Keranen’s team scrambled to install three seismometers around Prague. They did so in time to capture the quake system in unprecedented detail. She says, “We got this beautiful image of the fault plane.” Within a week, her team and other scientists had placed a total of 25 devices around the fault zone. One is buried in the Reneaus’ backyard. Now, having completed a yearlong study (just published in the journal Geology), Keranen’s research indicates the Oklahoma earthquakes were likely attributable to underground injection of wastewater derived from “dewatering,” separating crude oil from the soupy brine reaped through a drilling technique that allows previously inaccessible oil to be pumped up. “Pretty much everybody who looks at our data accepts that these events were likely caused by injection,” Keranen concludes.

“We still feel tremors weekly,” complains Joe Reneau. “They rattle our windows.” The couple hasn’t bothered to rehang family photos in their living room. Instead, the framed snapshots are stacked in tidy piles on a coffee table.

Such seismic activity isn’t normal here. Between 1972 and 2008, the USGS recorded just a few earthquakes a year in Oklahoma. In 2008, there were more than a dozen; nearly 50 occurred in 2009. In 2010, the number exploded to more than 1,000. These so-called “earthquake swarms” are occurring in other places where the ground is not supposed to move. There have been abrupt upticks in both the size and frequency of quakes in Arkansas, Colorado, Ohio, and Texas. Scientists investigating these anomalies are coming to the same conclusion: The quakes are linked to injection wells. Into most of them goes wastewater from hydraulic fracking, while some, as those in Prague, are filled with leftover fluid from dewatering operations.