Fracking triggered hundreds of small earthquakes along a previously unmapped fault in eastern Ohio late last year, according to a new study to be published in the journal Seismological Research Letters.

Looking at data from National Science Foundation seismographs located near fracking sites, scientists from Instrumental Software Technologies, Inc. (ISTI) and the Ohio Department of Natural Resources (ODNR) were able to make direct connections between at least 400 small "micro-earthquakes" and nearby fracking operations.

According to the Associated Press:

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.

"The earthquakes started shortly after fracking started on the wells and ended about two months after fracking ended," lead author Paul Friberg, of ISTI, told The Weather Channel. "There are no seismologists who have reviewed our work who think they were unconnected."

LiveScience reports that "because the earthquakes line up in an east-west direction in ancient crystalline rocks beneath the Utica Shale, Friberg and his co-authors think the fracking activated a small, unknown fault. The fracking water could have 'greased' the fault, unclamping the fracture and allowing it to slip."

This is not the first time tremors have been linked to the practice of drilling for shale oil and gas. Earlier this year, the ODNR announced new, stronger permit conditions for drilling near faults or areas of past seismic activity, in response to small earthquakes in Poland Township that showed a probable connection to fracking near a previously unknown microfault.

And in May, the U.S. Geological Survey and the Oklahoma Geological survey documented a phenomenon known as "injection-induced seismicity," which occurs  when fracking wastewater lubricates underground fault lines.

Friberg said he hopes the research, which will be published online starting tomorrow and in the November issue of Seismological Research Letters, will lead to further investigation of how fracking affects geology.