A high pressure gas line crosses over a canal in an oil field over the Monterey Shale formation where gas and oil extraction using hydraulic fracturing, or fracking, is on the verge of a boom on March 23, 2014 near Lost Hills, Calif.

State geologists in Ohio have for the first time linked earthquakes in a geologic formation deep under the Appalachians to gas drilling, leading the state to issue new permit conditions in certain areas that are among the nation's strictest.

A state investigation of five small tremors in the Youngstown area, in the Appalachian foothills, last month has found the high-pressure injection of sand and water that accompanies hydraulic fracturing, or fracking, in the Utica Shale may have increased pressure on a small, unknown fault, said State Oil & Gas Chief Rick Simmers. He called the link "probable."

While earlier studies had linked earthquakes in the same region to deep-injection wells used for disposal of fracking wastewater, this marks the first time tremors have been tied directly to fracking, Simmers said. Five seismic events in March were all part of what was considered a single event and couldn't be easily felt by people.

The state's new permit conditions are perhaps the most cautious yet put in place in the nation, he said.

Glenda Besana-Ostman, a seismologist with the U.S. Department of the Interior's Bureau of Reclamation, confirmed the finding is the first in the region to suggest a connection between the quakes and the actual extraction of oil and gas, as opposed to wastewater disposal. A deep-injection well in the same region of Ohio was found to be the likely cause of a series of quakes in the same region of Ohio in 2012.

Under the new permit conditions, all new drilling sites in Ohio within 3 miles of a known fault or seismic activity of 2.0 magnitude or higher will be conditioned on the installation of sensitive seismic-monitoring equipment. Results will be directly available to regulators, Simmers said, so the state isn't reliant on drilling operators providing the data voluntarily.

If seismic activity of 1.0 magnitude or greater is felt, drilling will be paused for evaluation. If a link is found, the operation will be halted.

"While we can never be 100 percent sure that drilling activities are connected to a seismic event, caution dictates that we take these new steps to protect human health, safety and the environment," said James Zehringer, director of Ohio's natural resources department.

Ohio has also imposed an indefinite drilling moratorium at the site of the March quakes. The state is allowing oil and gas extraction to continue at five existing wells at the site.

The Utica Shale lies beneath the better-known Marcellus Shale, where energy companies have drilled thousands of unconventional gas wells in Pennsylvania, Ohio and West Virginia in recent years.

The Marcellus is considered to be one of the richest natural gas reserves in the world. Drillers have only recently begun to tap into the deeper Utica.

--By The Associated Press