Tended to coincide with nearby activity
The quakes fell along a fault lying directly under three hydraulic fracturing operations and tended to coincide with nearby activity, researchers found. About 190 quakes were detected in a single three-day period last October, beginning within hours of the start of fracking. None of the quakes was reported felt by people.
Shawn Bennett, a spokesman for the Ohio Oil & Gas Association, said the industry is looking at the issue nationally but wants more information on what caused the Ohio. He said human-caused earthquakes are "extremely rare," whereas 1.3 million tremors of similar magnitude happen naturally around the globe every year.
Ohio Department of Natural Resources spokeswoman Bethany McCorkle said the state has installed seismic monitoring equipment throughout eastern Ohio over the past year and is keeping close watch for earthquakes strong enough to be felt.
Fracking involves the high-pressure injection of water, sand and chemicals into shale to break up the rock and release trapped oil and gas.
Rowena Lohman, an assistant professor of geophysics at Cornell University who was not involved in the study, said some faults cannot be discovered until underground activity is attempted. She said the latest findings can be used to try to prevent worse quakes.
"We've known for a really long time, going back to the '70s, that when you do any subsurface manipulation you cause small earthquakes," she said. "The big question is: Are we doing something now that increases the probability that it will induce larger quakes?"