Earthquakes never used to happen in Poland Township, Ohio — or, at least, they were never identified. But then the fracking started. In March of 2014, the township saw 77 earthquakes occur, says Robert Skoumal, a seismologist at Miami University. These earthquakes were so small that most went unnoticed by the area's 15,000 inhabitants. But when the hydraulic fracturing operations stopped, so did the earthquakes, Skoumal says — and "no earthquakes in this area have been observed since."

One the largest earthquakes ever induced by hydraulic fracturing in the United States

Skoumal is one of the researchers behind a new study that links a rare "felt" earthquake — an earthquake strong enough that humans can feel it — to hydraulic fracturing operations that took place in Poland Township in 2014. Hydraulic fracturing, or fracking, is the process by which sand, water, and various chemicals are injected into the ground to extract natural gas from shale rock deep underground. It very rarely leads to earthquakes, and "only a handful of fracking operations worldwide have induced felt earthquakes," Skoumal says. But in March of 2014, Poland Township experienced a series of earthquakes, including one — a magnitude 3 earthquake — that was "one the largest earthquakes ever induced by hydraulic fracturing in the United States."

In the study, which will be published tomorrow in the Bulletin of the Seismological Society of America, Skoumal and his team of researchers compared the timing of the Poland Township earthquakes to the fracking operations. They also compared the location of the earthquakes in relation to the fracking wells. This analysis helped them determine that a relatively small portion of the fracking operation — the northeast portion — was responsible for the earthquakes in Poland Township.

hydraulic fracturing could potentially trigger larger magnitude earthquakes

"The science is sound," says Danielle Sumy, an earthquake researcher at the Incorporated Research Institutions for Seismology, who did not participate in the study. And "the findings are quite novel." Hydraulic fracturing, Sumy explains, usually causes very small earthquakes that aren’t felt by humans. The novelty of the study therefore lies in the fact that the magnitude 3 earthquake is one the largest earthquakes ever thought to be induced by hydraulic fracturing in the United States. Moreover, she says, the findings show that hydraulic fracturing could potentially trigger larger magnitude earthquakes than previously observed in the US.

So far, there have only been a handful of fracking-induced earthquakes in the world, Skoumal says. And although hydraulic fracturing has caused larger earthquakes outside of the US — in British Columbia, for instance — they were still relatively small. "In Ohio, we think induced earthquakes are caused by the activation of a pre-existing fault located near the fracking operation," Skoumal says. The hydraulic fracturing operations likely "clock-advanced" the occurrence of this earthquake, Sumy says, meaning that it's possible that the earthquakes would have happened anyway, a long time from now.

"may have been felt by only a few people and likely cause little or no damage."

Unfortunately, identifying faults prior to fracking is very difficult and expensive, Skoumal says. So, even though it isn’t recommended to frack near known faults, fracking continues to takes place near ones that have yet to be identified.

Still, the researchers say fracking-induced earthquakes aren't cause for alarm. "People in areas with ongoing hydraulic fracturing should not panic about induced earthquakes," Skoumal says. "The chances that hydraulic fracturing operation will induce felt seismicity is rare." Sumy agrees: "the largest earthquake may have been felt by only a few people and likely caused little or no damage in the nearby regions." Moreover, both Sumy and Skoumal say that increased communication between industry, scientific bodies, and regulatory bodies will go a long way toward reducing the likelihood of these events in the future.

Since the earthquake, the Ohio Department of Natural Resources has announced more stringent regulations that it hopes will reduce the likelihood of future induced earthquakes. "While we can never be 100 percent sure that drilling activities are connected to a seismic event," natural resources department director James Zehringer said in a statement last April, "caution dictates that we take these new steps to protect human health, safety, and the environment."