A natural gas fracking site. Photo by Daniel Foster, CC BY-NC-SA 2.0

Following a 3.0 magnitude earthquake on 10 March 2014 that occurred near hydraulic fracturing (fracking) sites in Poland Township, Ohio, the Ohio Department of Natural Resources halted nearby fracking activities. At the time, the department speculated that the earthquake was related to fracking, but scientists have now found more substantial evidence for this link.

In a paper published 5 January in the Bulletin of the Seismological Society of America, researchers report that fracking was most likely the cause of the 3.0 local magnitude earthquake, as well as 77 newly found much smaller quakes—which were not felt by the area’s residents—that occurred in the previous week.

The Ohio earthquake is now thought to be the largest earthquake caused by fracking in the United States, Robert Skoumal, lead author of the paper and a seismologist at Miami University in Ohio, told Eos. He stressed, however, that these fracking-induced “felt earthquakes” are extremely rare.

“[There are] only a handful of reported cases worldwide,” Skoumal said.

Fracking-Related Earthquakes in the United States

Scientists know that the reinjection of fracking wastewaters into the ground can cause small earthquakes, but there are no wastewater injection wells near Poland Township, Skoumal noted. Instead, the new paper gives more weight to the idea that fracking itself—the act of injecting water, sand, and other chemicals into rock to ease the extraction of oil and gas—can induce seismicity.

In the United Kingdom and Canada, scientists have found evidence of earthquakes directly related to fracking. However, little research has been done in the United States, said David Eaton, a seismologist at the University of Calgary who was not involved in the research.

“This paper is one of the first to document induced seismicity in the [United States] directly associated with hydraulic fracturing,” he said.

Oil and gas companies usually use fracking to extract hydrocarbons from dense material, most often shale or sandstone. Fracking creates high pressures within the rocks, which can expand existing fractures or create new fractures. These fractures are tiny and almost always result in microearthquakes registering between -3 and 0 magnitude, Skoumal said.

So what made the Poland Township earthquake so relatively large? “We think that there has to be a preexisting fault located nearby that is critically stressed and optimally oriented for it to be triggered by hydraulic fracturing,” Skoumal explained.

The Poland Township Earthquakes

In Poland Township, a 55-square-kilometer chunk of Ohio, no earthquakes had ever been identified until fracking began.

“Natural earthquakes do occur in Ohio, but those sequences can be differentiated from induced sequences,” Skoumal said.

The pattern of Poland Township’s earthquake swarms did not match natural patterns, he explained. Normally, Ohio’s seismicity commonly follows a “mainshock/aftershock” pattern, with one larger earthquake followed by several smaller quakes. In this case, the largest earthquake in the sequence followed the slew of small quakes. The number of quakes was also unusual for Ohio. Furthermore, the earthquakes all occurred near the well—800 meters below the northeastern extent of the operation—while fracking was taking place.

To get a handle on the scope of the induced seismicity, the researchers turned to a database of continuous seismic activity, recorded by a network of seismic stations that dotted the Ohio landscape. They looked for signatures similar to the magnitude 3.0 earthquake and identified 77 smaller but related quakes. They then compared the timing and location of these earthquakes to drilling reports of nearby fracking wells available from the Ohio Department of Natural Resources.

“No earthquakes had ever been identified in Poland Township prior to fracking, and after the operation ceased, no earthquakes have been identified in the area since,” Skoumal said.

Analysis of the seismic signatures generated by the earthquakes in Poland Township also allowed Skoumal’s group to pinpoint the fault likely triggered by fracking. It lies about 3 kilometers underground, near the township.

Better Methods

The paper highlights “the power of the methods used by the authors,” Eaton said. “More significantly, it convincingly shows the potential relationship between induced earthquakes and hydraulic fracturing.” This information may help scientists who have begun to investigate the connections between fracking processes and earthquakes elsewhere, such as Texas, Oklahoma, and Colorado.

Skoumal stressed that the Ohio Department of Natural Resources made the right call by halting fracking activities after the quake and that there was no wrongdoing by the operators of the Poland Township fracking well. Since the event, the Ohio Department of Natural Resources has announced tighter restrictions on fracking in the area.

—JoAnna Wendel, Staff Writer

Citation: Wendel, J. (2015), Ohio earthquake directly tied to fracking, Eos, 96, doi:10.1029/2015EO021955.

Text © 2015. The authors. CC BY-NC 3.0
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