AZLE — The earth is literally jumping along a stretch of real estate from Fort Worth’s Eagle Mountain Lake and Azle to the Parker County communities of Springtown and Reno.Seven mild earthquakes have struck in the past month, one as recently as Thursday morning off East Peden Road in far north Fort Worth. The tremors haven’t caused damage or injuries, and they haven’t rattled residents.But every time her brick house shakes, Earlene Clouse reaches for her writing pad to keep a running tab of seismic events.“One sounded like a sonic boom,” the retired Azle teacher said of a particularly noteworthy quake at about 1:55 p.m. Nov. 9. “ BOOM!” That was the strongest, registering a magnitude of 3.0, according to the U.S. Geological Survey. Others caused something to pop in the rafters and near a living room desk. But no dishes have broken, and the windows and Sheetrock haven’t cracked. “It’s not like California, where they have big ones,” said Clouse, who once showed her second-graders a film about devastating earthquakes in distant lands.Her husband, John, a retired Texas Workforce Commission supervisor, said he misses many of the tremors because he regularly snoozes in a thick-cushioned easy chair that somehow absorbs the sudden movement. He wasn’t disturbed to learn that his homeowners policy with Farmers Insurance will not pay for earthquake damage or that the company won’t offer add-on coverage.The Clouses — and others interviewed at Howell’s Cafe in nearby Springtown, where the earthquakes have become fodder for morning coffee chatter — insist that they are not worried in the least. The quakes have occurred a few miles from injection wells drilled to dispose of huge amounts of wastewater from natural gas wells in the Barnett Shale.Geophysicists and seismologists have linked quakes in normally calm areas of Arkansas, Texas, Ohio, Oklahoma and Colorado to below-ground wastewater injection, according to Geoffrey Abers of Columbia University and Elizabeth Cochran of the U.S. Geological Survey, writing this year in the journal Geology.The energy industry stresses that hydraulic fracturing, used to tap hitherto unreachable gas deposits in shale rock, has not induced seismic activity. And the scientists agree. “Although it may seem like science fiction, man-made earthquakes have been a reality for decades,” the Geological Survey said in a July report. Such tremors can be induced by impounding water for reservoirs, mining on the surface or underground, withdrawing fluids and gas from the subsurface and, it added, injecting fluids into underground formations.But it can take years to determine a correlation between a particular activity and a quake, or a swarm of quakes. Even then there’s not always consensus among experts.Scientists look for answersA magnitude-5.7 earthquake struck Nov. 6, 2011, near the central Oklahoma town of Prague (pronounced “praig”), not far from wastewater injection wells. Two people suffered minor injuries, 14 homes sustained at least some damage, three portions of U.S. 62 buckled, and the turret on a building at St. Gregory’s University in nearby Shawnee collapsed, according to news reports by the Los Angeles Times and others.Two years later, scientists are taking sides on three theories about what caused the Prague tremor. Katie Keranen, a University of Oklahoma seismologist, maintains that increased fluid pressure at two wastewater injection wells lubricated a geological fault, triggering a magnitude-5 foreshock that in turn prompted the magnitude-5.7 quake, as well as aftershocks.But the Oklahoma Geological Survey says the Prague tremors were naturally occurring earthquakes.A third hypothesis, supported by Art McGarr, who heads the U.S. Geological Survey’s induced seismic activity unit, suggests that the vast amounts of wastewater from the two injection wells cited by Keranen and a third well — less than a mile away but not noted by her — were enough to cause the quakes.In 2011, University of Texas seismologist Cliff Frohlich published a paper with scientists at Southern Methodist University linking a swarm of 2009 quakes to two injection wells owned by Chesapeake Energy at Dallas/Fort Worth Airport. Three months later, news reports quoted officials of the National Boy Scout Museum in neighboring Irving as saying that the tremors caused an estimated $100,000 in damage. Museum officials did not return calls seeking details.Chesapeake closed both wells months later as a precaution while maintaining that a link with the tremors had not been scientifically proved.Some of the strongest evidence of injection wells inducing quakes arose in Arkansas from activity in the Fayetteville Shale near a deep but previously unknown fault.The area, which includes the city of Conway, experienced 1,350 earthquakes from September 2010 through June 2011. The most powerful was a magnitude-4.7 tremor on Feb. 28, 2011. “It went from a novelty to a kind of a nuisance,” said Scott Ausbrooks, geohazards supervisor of the Arkansas Geological Survey. “I live in the area. I was getting up three, four times a night. People texted me asking when the shaking was going to stop.”‘Hard to predict’More than 3,000 fracking wells were drilled in Arkansas over the past five years, and all needed a place to dispose of tons of wastewater. But the quakes were concentrated along the Guy-Greenbrier fault, where four injection wells operated. In an unprecedented move, the Arkansas Oil and Gas Commission voted 6-0 in July 2011 to close the wells. And the ban seems to have worked.In 2012, the number of tremors near the fault dropped to eight, and there have been only two this year, said Ausbrooks, who is sleeping more soundly these days.Although other parts of the state have injection wells, the quakes occurred mainly along the newly discovered fault. So why some areas and not others?“The general answer is that there’s a lot we don’t understand about them,” McGarr said. “There are 30,000 wastewater wells in the United States, and most don’t produce earthquakes. Maybe 30 or 40 do.”“It’s not easy to identify faults likely to fail,” he said. “Even if you know faults are there, it’s not clear which might slip in an earthquake and which are relatively benign. To be honest, we really don’t understand why so many wells don’t produce earthquakes. We have a ways to go.”So what’s in North Texas’ future?“I think that if they continue injecting large amounts of wastewater, it may lead to greater-magnitude earthquakes,” McGarr said. “But it’s hard to predict, and all indications are that Texas is less prone than other parts of the country” to powerful earthquakes.Wastewater limitsThat uncertainty has made it difficult, if not impossible, to determine guidelines for mitigating these problems.Asked whether it had closed any injection wells because of the likelihood of quakes, the Texas Railroad Commission replied by email: “No. Commission staff have not closed any wells due to theories proposing a causation to seismic events.”The commission said operators face limits on how much wastewater they can inject — 25,000 barrels a day in most areas of the Barnett Shale, 5,000 in shallower formations. But the commission relies on self-reporting on an annual basis, which means there could be a long lag after a quake or a cluster of quakes.Who are the operators? They range from big players like Chesapeake, XTO and Devon to far smaller concerns like Bridgeport Tank Trucks. Since the wells can cost about $10 million to drill, a closure is a sizable loss for mom and pop operators. Bridgeport, which owns an injection well near Springtown, did not return calls seeking comment for this report.With no highly destructive quakes, few see a real danger.“Being big enough to be felt, that’s a public relations problem [for energy companies],” McGarr said. “But so far, the problems in Texas have been relatively small.”Making jokesOver meatloaf, mashed potatoes and black-eyed peas, the lunch crowd at Howell’s Cafe gave first-person accounts or joked about the earth moving — having more to do with biology than seismology.A cook named Nancy Shearman was convinced that a heavy tree limb had fallen on her home. Barry Bobo said the only person worried about the quakes was a woman who discovered sinkholes on her property, a phenomenon that geologists say was not likely related to seismic activity.Bobo, who runs a construction company and a resale shop, said he got in hot water for telling a local TV station, “I don’t know if it was an earthquake or my wife’s snoring.”Soon afterward, his wife made a tongue-in-cheek Facebook post that her husband was looking for a new place to live.On Thursday, Bobo said he’s still home. In earthquake country.
Barry Shlachter, 817-390-7718 Twitter: @bshlachter