A swarm of recent earthquakes that has rattled residents in and around Irving, Texas, has sparked a disagreement among seismologists over how to determine whether fracking could be to blame.
On the one side, the seismologist for the regulatory agency overseeing the state's oil and gas industry said he sees no connection between the two.
“There are no oil and gas disposal wells in Dallas County,” Craig Pearson, the seismologist for the Texas Railroad Commission, said in a statement. “And I see no linkage between oil and gas activity and these recent earthquakes in Irving.”
But a geophysicist from the U.S. Geological Survey said an investigation must look at all possibilities.
“It’s too early for us to say that we don’t see any connections yet,” said Robert Williams, a coordinator with the U.S. Geological Survey Earthquake Hazards Program in Golden, Colorado. “We don’t want to rule anything out at this point.”
And an investigation into whether fracking could be responsible should look at wells over a greater area than the Railroad Commission would consider, Williams said. Recent studies have shown larger distances between wastewater disposal wells and the earthquakes associated with them, he said.
Seventeen earthquakes have been recorded around Irving, Texas, near the old Texas Stadium, since Jan. 6 and 38 since the beginning of last year — all for an area that has historically seen few earthquakes. They are the latest in a series of earthquakes since 2008. Researchers found a plausible connection between earlier earthquakes and waste water disposal wells, and the question now is whether the latest earthquakes are occurring naturally or linked to fracking.
A team from the Southern Methodist University in Dallas has installed 22 new seismographs in the area, some of which are feeding directly back to the U.S. Geological Survey National Earthquake Information Center in Golden, to pinpoint precise locations of the quakes and then to look for the active fault or faults.
“We’re really in the dark about faults right there in Irving, Texas, that might be responsible,” Williams said. “We don’t know the fault structure really at all."
The researchers are in the first stage of trying to determine why the earthquakes, all of which have been small, are occurring.
"Only after we get that data will we be in a position to investigate the potential cause of the earthquakes," said Heather DeShon, an associate professor of physics at Southern Methodist University, in a statement.
The seismologists will need an additional month of research to better understand the fault line, Brian Stump, the chairman of geological sciences of the university's Huffington Department of Earth Sciences, told the Irving City Council at its meeting on Thursday.
"The earthquakes are from those stresses," he said. "The question is, 'Is it just a natural process? Or is there some human activity?'"
Fracking or hydraulic fracturing is a process used to maximize the extraction of oil and natural gas. A mixture of water and chemicals is pumped into wells at high pressure to fracture the rock so that oil or natural gas can flow, according to the U.S. Environmental Protection Agency. Once the fracking is completed, the fluids may be injected into waste-disposal wells.
There are no disposal wells in Dallas County, where the earthquakes have occurred, according to the Railroad Commission. The closest well is 10 miles away. Models of subsurface flow used to establish rules related to earthquakes provide no evidence that there would be increased pressure beyond 5.6 miles or a 100-square-mile area, according Railroad Commission spokeswoman Ramona Nye.
In addition, the commission notes that two gas wells near the Irving earthquakes are inactive; one has not produced since 2012, the other never produced.
But Williams with the USGS said that new research published last year in the journal Science showed a potential connection between high volume waste water disposal wells in Oklahoma and earthquakes generated 12 to 18 miles away. The lead author, Katie Kernanen, is an assistant professor of seismology at Cornell University in New York.
Pearson does not believe that the Oklahoma study is related to the earthquakes in Texas, his office responded. Pearson began reviewing the earthquake data in November, and is coordinating an exchange of information between the seismic researchers at Southern Methodist University and the oil and gas industry, according to Nye, the commission's spokeswomen.
"Dr. Pearson is focused on what’s happening here in Texas," she wrote in an email.
"Specifically, the disposal well operation more than 10 miles away from Irving is not disposing of high volumes, and the geology in Texas is different from geology in Oklahoma," she wrote.
There were more than 400,000 active oil and gas wells in Texas as of the end of December and more than 35,000 wastewater injection wells, according to the commission.
At what the Texas Railroad Commission defines as an “injection well,” the fluid is re-injected to extract additional oil from depleted reservoirs. At a “disposal well,” the fluid is injected into areas that are not producing oil or gas. The vast majority of wells in Texas are injection wells; there are about 7,500 disposal wells.
There have been more than 120 earthquakes in North Texas since 2008, according to Southern Methodist University. All of them have been considered small, with the largest occurring in 2013 at magnitude 3.7. Before that an earthquake large enough to be felt had not been reported since 1950.
Stump told the Irving City Council that scientists could not rule out larger earthquakes in the future, some damaging.
“I don’t like it. It shouldn’t be happening. Somebody should be doing something,” said one of the dozens of residents who attended the meeting, Suzye Marino. “And I want it done quick because who knows when the big 4.5 or 5.0 might hit?
The recent earthquakes are the fourth in a series of clusters: near the Dallas/Fort Worth International Airport in 2008 and 2009, in Cleburne between 2009 and 2010 and in the Reno-Azle area between 2013 and 2014.
Southern Methodist University researchers found that waste water wells were a plausible cause for the clusters at the Dallas/Fort Worth airport and in Cleburne. A report on the Reno-Azle area has not been published yet.
The researchers cautioned that there were still many unanswered questions. Though they found a correlation between the earthquakes near the Dallas/Fort Worth International Airport and saltwater injection wells, for example, they said they did not have complete information about how porous the rocks were, the path the fluids took, and how that might induce an earthquake.
The study noted there were more than 200 saltwater disposal wells active in the production of natural gas in the area where the Barnett Shale formation traps gas deposits in subsurface rock.
“If the DFW earthquakes were caused by saltwater injection or other activities associated with producing gas, it is puzzling why there are only one or two areas of felt seismicity," the study said.
Though recent studies have looked at the relation between earthquakes and disposal wells, a much smaller number have looked at the fracking itself. One published in January in The Bulletin of the Seismological Society of America linked earthquakes outside of Youngstown, Ohio, in March to fracking.
“These were attributed directly to the hydraulic process itself,” said one of the study’s authors, Robert Skoumal, a graduate student at Miami University in Oxford, Ohio. “This is not waste water injection. This is hydraulic fracturing that reactivated a pre-existing fault."
Ben Russell contributed to this article.