Ohio geologists have found a probable connection between fracking and several mild earthquakes in a region that had never experienced a temblor until recently, according to a state report.

The report, which coincided with Ohio's announcement of some of the nation's strictest limits on fracking near faults, marked the strongest link to date between nerve-rattling quakes and hydraulic fracturing -- the process of firing water, sand and chemicals into the earth to extract oil and natural gas from ancient rock.

Last month, the state shut down Hilcorp Energy's fracking operation near the Pennsylvania border after five earthquakes, including one magnitude 3 temblor that shook many Ohioans awake.

Federal scientists have previously linked earthquakes in part to the use of injection wells, where post-fracking wastewater is forced back deep into the earth for storage. None of the seven wells near the Ohio quakes were used for waste disposal, leaving Ohio scientists to go a step further to find a significant relationship between the initial blast of fluid and the earthquakes shortly thereafter.

They "believe the sand and water injected into the well during the hydraulic fracturing process may have increased pressure on an unknown microfault in the area," the Ohio Department of Natural Resources said in a statement about the operation in Poland, Ohio.

The new rules require companies to install "sensitive seismic monitors" before beginning to drill sideways into underground rock "within 3 miles of a known fault or area of seismic activity greater than a 2.0 magnitude."

Humans can generally feel earthquakes in excess of magnitude 3.

Drilling would be suspended pending investigation whenever the monitors detect anything above magnitude 1.