A series of earthquakes in Poland Township, Ohio, were triggered by hydraulic fracturing operations nearby, according to new research published by the Bulletin of the Seismological Society of America (BSSA).

Five earthquakes, ranging from magnitude 2.1 to 3.0, were recorded in the area in March 2014. All of them occurred within one kilometer (0.6 miles) of a group of oil and gas wells operated by Hilcorp Energy, which was conducting fracking operations at the time.

Because of the proximity of a magnitude 3.0 quake to one of the Hilcorp wells, the Ohio Department of Natural Resources immediately halted operations at the site.

The process of fracturing shale rock in order to extract gas and oil normally results in micro-earthquakes much smaller than humans can feel, and the researchers pointed out that it remains rare for fracking to cause larger earthquakes. However, with advances in seismic monitoring and an increase in fracking activity, the number of earthquakes — felt and unfelt — associated with hydraulic fracturing has risen in the past decade.

In Ohio, the nearby fracking did not create a new fault; it activated an existing fault that was not known about previously.

"We just don't know where all the faults are located," said Robert Skoumal, one of the researchers. "It makes sense to have close cooperation among government, industry and the scientific community as hydraulic fracturing operations expand in areas where there's the potential for unknown pre-existing faults."

Robert Skoumal, Michael Brudzinski and Brian Currie, from Miami University in Ohio, have detailed their findings in a paper titled 'Earthquakes Induced by Hydraulic Fracturing in Poland Township, Ohio', published in the February/March issue of BSSA.