State researcher dismisses Virginia Tech study of quakes
A team of Virginia Tech University researchers found that Oklahoma’s earthquakes have been caused by saltwater disposal wells up to 77 miles away and that more action is needed to address the ongoing earthquake swarm.
An Oklahoma researcher, however, dismissed the report as out of date and for failing to account for the state’s complex geology.
The Virginia Tech study developed a model to analyze the earthquakes that rumbled Oklahoma from 2011 through 2016. The report showed that earthquakes of less than magnitude 3.0 declined along with saltwater injection rates in 2016, but that the rate of stronger earthquakes did not show the same response.
“Our study suggests that decreasing the volume of wastewater going into the Arbuckle will further help to reduce the correlation between wastewater injection and earthquakes,” researcher Ryan M. Pollyea said in an interview with The
Oklahoman. “Continuing to decrease wastewater injection is important. Those are the steps that are being taken.”
The state’s overall earthquake rate fell more than 30 percent from 2015 to 2016, although the state experienced two of its most powerful quakes on record in 2016. The study did not include data from 2017, where both the overall rate and the rate of stronger earthquakes fell by about 50 percent from the previous year.
“It feels like the report was written well before the data was submitted, and it misses a few things,” said Jeremy Boak, director of the Oklahoma Geological Survey. “I’m underwhelmed by the article. They’ve quantified it in a statistical way, but they’ve also done it in a way that ignores some geology.”
Finding faults
While earthquakes have occurred throughout much of central and northwestern Oklahoma, Boak said the claim that injection wells have caused earthquakes up to 77 miles (or 125 kilometers) away ignores the large faults that cross the state.
“One problem is they don’t take any cognition of major faults that clearly segment the seismic activity,” Boak said. “The only way you can get to 125 kilometers is by stretching across from the central Cherokee Platform all the way over to northwest of Fairview where the Galena Township fault is located. I think there’s a much closer proximity of high injection that can be driving the earthquake activity in the west.”
The report recommends further reduction of saltwater disposal in the Arbuckle formation, which is the deepest sedimentary rock formation underlying most of the state.
“I think there needs to be more study in to how the fluid pressure is moving through the Arbuckle,” Pollyea said. “How much reduction is needed is a function of how much pressure is moving underground.”
Boak pointed out, however, that the report does not include Oklahoma Corporation Commission rules that cut Arbuckle injection volumes by 40 percent. Oklahoma Geological Survey researchers also are studying pressure and water movement in the Arbuckle.
While the Virginia Tech research was critical of Oklahoma’s efforts to reduce seismicity, that concern doesn’t seem to be shared by the U.S. Environmental Protection Agency.
In December, the agency sent Oklahoma’s Corporation Commission an evaluation of its underground injection control program performance during state fiscal years 2016 and 2017, noting the state’s efforts to reduce seismicity issues had been “impressive.”
“We again commend the Oklahoma Corporation Commission’s impressive efforts to address seismicity in the state and are pleased with the dramatic decrease in seismic activity over the last year,” William H. Honker, director of the EPA’s Water Division for Region 6, wrote as part of his cover letter on the evaluation.
I’m underwhelmed by the article. They’ve quantified it in a statistical way, but they’ve also done it in a way that ignores some geology.” Jeremy Boak, director of the Oklahoma Geological Survey