Several minor earthquakes reported in Ohio in the past year — including one on Saturday — have taken place near an injection well where wastewater from gas drilling is pumped underground.
But after the latest tremor, Ohio Department of Natural Resources Director Jim Zehringer told reporters that fracking, used to extract the gas, is not causing the quakes.
"The seismic events are not a direct result of fracking," he said.
Fracking, also known as hydraulic fracturing, involves injecting a pressurized mix of water and other substances into the rock to release trapped natural gas.
What the industry refers to as flowback, consisting of highly salty water, is produced with the gas when wells initially come online. In some jurisdictions, this wastewater is sent underground for disposal using injection wells.
Zehringer said state officials have temporarily halted the underground disposal of drilling wastewater within eight kilometres of the Youngstown injection well.
Some experts say the wastewater, mostly brine, is putting pressure on a fault line at Youngstown.
The Youngstown Vindicator newspaper has quoted state seismologist Mike Hansen as saying there could be more earthquakes as it could take days or weeks until the pressure is completely relieved.
Thousands of litres of brine were being injected into the well daily until its owner, Northstar Disposal Services LLC, agreed Friday to stop injecting brine into the earth as a precaution while authorities assess any potential links to the quakes.
The 4.0-magnitude quake reported Saturday afternoon in McDonald, outside of Youngstown, was the 11th in a series of minor earthquakes in area since last March, many of which have struck near the Youngstown injection well.
The quake caused no serious injuries or property damage, but was strong enough to shake small objects in the homes of areas residents.