State regulators have for the first time have linked earthquake activity in eastern Ohio to hydraulic fracturing, confirming the suspicions of activists pushing unsuccessfully for a drilling ban.
State Oil & Gas chief Rick Simmers said the state has halted drilling indefinitely at the site near Youngstown where five minor tremors occurred in March following investigative findings of a probable link to fracking.
A deep-injection well for fracking wastewater was tied to earthquakes in the region in 2012.
Mr Simmers says Ohio will require sensitive seismic monitoring as a condition of all new drilling permits within three miles of a known fault or existing seismic activity of 2.0 or greater.
A seismologist with the US Department of Interior said it is the first time seismic activity has been linked to Marcellus shale exploration which has swept the north-eastern United States.