New Research Links Scores of Earthquakes to Fracking Wells Near a Fault in Ohio

Not long after two mild earthquakes jolted the normally steady terrain outside Youngstown, Ohio, last March, geologists quickly decided that hydraulic fracturing operations at new oil-and-gas wells in the area had set off the tremors.

Now a detailed study has concluded that the earthquakes were not isolated events, but merely the largest of scores of quakes that rattled the area around the wells for more than a week.

The study, published this week in The Bulletin of the Seismological Society of America, indicates that hydraulic fracturing, commonly called fracking, built up subterranean pressures that repeatedly caused slippage in an existing fault as close as a half-mile beneath the wells.

The number and intensity of fracking-related quakes have risen as the practice has boomed. In Oklahoma, for example, quakes have increased sharply in recent years, including the state’s largest ever, a magnitude 5.7 tremor, in 2011. Both state and federal experts have said fracking is contributing to the increase there, not only because of the fracking itself, but also because of the proliferation of related wells into which fracking waste is injected. Those injection wells receive much more waste, and are filled under high pressure more often, than oil or gas wells, and the sheer volume of pressurized liquids has been shown to widen cracks in faults, raising the chances of slippage and earthquakes.

The authorities in Ohio ordered a halt to fracking at seven wells on March 10 after the two biggest quakes there, measured at magnitudes 2.8 and 3, were felt in Poland Township, about 10 miles south of Youngstown on the Pennsylvania border.

A spokeswoman for the state’s Department of Natural Resources, Bethany McCorkle, said Wednesday that the wells remained in production but that further fracking had been banned.

Wells for fracking are typically sunk horizontally into thin bands of shale deep beneath the surface, and a soup of water, chemicals and sand is injected under intense pressure to fracture the rock and release trapped oil and gas.

The Poland Township study concluded that only two of the seven wells, with segments closest to the fault, were inducing the earthquakes. “It seems that only the segments that were within about a thousand yards from where the fault was produced earthquakes,” Michael R. Brudzinski, a professor and seismologist at Miami University in Oxford, Ohio, said in a telephone interview. “It appears you have to be quite close to the fault for fracking operations to trigger earthquakes. Having that sort of information helps us to see that this stuff is pretty rare.”

Dr. Brudzinski researched the Poland Township quakes with a Miami University geologist, Brian Currie, and a graduate student who is the study’s lead author, Robert Skoumal.

In Poland Township, an analysis of seismological data found 77 well-related earthquakes from March 4 to March 12, the four largest of them on March 10. All occurred about 1.9 miles underground, along a horizontal fault that at times ran less than a half-mile under wells where fracking was underway.

Dr. Brudzinski said the study underscored the need to monitor wells in seismically active areas, something Ohio has since required.