(CNN) -- State leaders have ordered that four fluid-injection wells in eastern Ohio will be "indefinitely" prohibited from opening in the aftermath of heightened seismic activity in the area, an official said.
Ohio Department of Natural Resources Director James Zehringer had announced on Friday that one such well -- which injects "fluid deep underground into porous rock formations, such as sandstone or limestone, or into or below the shallow soil layer," the U.S. Environmental Protection Agency explains -- was closed after a series of small earthquakes in and around Youngstown.
Then on Saturday, a magnitude 4.0 earthquake struck that released at least 40 times more energy than any of the previous 10 or more tremors that had rattled the region in 2011.
Andy Ware, deputy director of Ohio's natural resources department, told CNN on Sunday that Zehringer and Gov. John Kasich subsequently ordered that four nearby injection well projects will not open in the coming weeks, as had previously been planned. They 'll be inoperational until a determination is made in an investigation of a possible link between the earthquakes and the fluid-injection wells, he added.
"They will (not open) until we are satisfied that the process can be safely resumed," said Ware.
Such disposal wells act as a disposal for waste fluid that is a byproduct of hydraulic fracturing, better known as fracking. That technology involves injecting water, sand and chemicals deep into the ground at high pressure to crack the shale and allow the oil or gas to flow.
Last Friday's order affecting the first well in Youngstown came six days after a magnitude 2.5 earthquake that struck that area around 1:24 a.m. on December 24. After Saturday's larger earthquake, scientists recommended that operations stop at all wells within a 5-mile radius of that original site.
"We need to get more information," Ware said.
The epicenter for Saturday's tremor was 5 miles northwest of Youngstown, 6 miles southeast of Warren and 55 miles east-southeast of Cleveland, the U.S. Geological Survey reported. According to the preliminary estimate, the earthquake struck 1.4 miles deep.
There was a lot of shaking "and a rumbling sound," said Jimmy Hughes, a former Youngstown police chief running for sheriff of Mahoning County. "I could see the house move. ... It seemed like the ground was moving. "
Ohio is far from the edges of Earth's major tectonic plates, with the nearest ones in the Atlantic Ocean and the Caribbean Sea, the U.S. Geological Survey explains on its website. Still, there are many known faults in this region, with the federal agency noting that it is likely there are additional "smaller or deeply buried" ones that haven't been detected.
While earthquakes are not unprecedented in the area, the rate of them in the past year has been unusual. That fact led Zehringer, the Ohio department head, to act late last week.
"While conclusive evidence cannot link the seismic activity to the well, Zehringer has adopted an approach requiring prudence and caution regarding the site," the natural resources department said Friday in a press release, explaining its decision to shut the first well.
Ben Lupo -- CEO of D&L Energy, an independent natural gas and oil exploration, production and marketing group that is affiliated with the first well that was closed -- recently told CNN affiliate WKBN that there's full cooperation with experts, though he expressed grave doubts that the injection wells were to blame for the quakes.
"We have approximately 1,000 wells between Ohio and Pennsylvania and we've never had a problem ... with an earthquake or spill," Lupo said.
Dr. Won-Young Kim, one of the Columbia University experts asked by the state to examine possible connections between fracking and seismic activity, said that a problem could arise if fluid moves through the ground and affects "a weak fault, waiting to be triggered." He explained the underground waste "slowly migrates" and could cause issues miles away, adding that the danger could persist for some time as the fluid travels and seeps down toward the fault.
"In my opinion, yes," the recent spate of earthquakes around Youngstown is related to a fluid-injection well, Kim stated -- though there has been no definitive determination, by the state or other authorities, indicating as much.
There have been "moderately frequent" reports of earthquakes in northern Ohio since the first recorded one was reported in 1823, the federal agency noted. A 1986 tremor, measuring magnitude 4.8, caused some damage. Another in 1998 measured a 4.5 and was centered in northwest Pennsylvania.
CNN's Greg Botelho, Susan Candiotti and Ross Levitt contributed to this report.