Northeastern Ohio has been rattled by close to a dozen earthquakes since last spring. It's not an area that is known for them.
Now, CBS News correspondent Michelle Miller reports that an expert on quakes says he believes they may have been man-made.
John Armbruster is a seismologist at Columbia University. Before March, there had never been a recorded earthquake in Youngstown, Ohio. Since then, there's been 11.
Residents call the new phenomenon "an experience."
The new earthquakes caused Ohio state officials to ask Armbruster to investigate.
"These earthquakes were sitting there waiting to happen. We have triggered these earthquakes," Armbuster said.
Armbruster believes the trigger was a Youngstown well that disposes of contaminated water trucked in from elsewhere in Pennsylvania and beyond. The water is a byproduct of oil and natural gas extraction, called "fracking."
The disposal well pumps thousands of gallons of the waste into rock a mile or more below. Armbruster says the fluid may have made its way into an earthquake fault line.
"Pumping the fluid into the fault encourages the fault to slip," Armbruster said.
Armbruster added that seismic readings allowed him to pinpoint the epicenter of a quake near the Youngstown well.
"It was about a kilometer from the bottom of the disposal well," Armbruster said.
Drilling companies and some scientists are skeptical. 177 similar wells in Ohio have operated without incident, and the technique has been used since the 1930s at more than 100,000 wells across the nation.
"It's happened with regulatory certainty, regulatory excellence, and it's the best way to take care of this waste stream," said Tom Stewart with the Ohio Oil and Gas Association.
Clusters of small earthquakes near wells in Oklahoma, Texas and Arkansas have also drawn scrutiny.
"First of all, the location of the earthquakes is quite close to the wells. Secondly, the timing of the waste water injection also coincides with the earthquakes," said Art McGarr with the U.S. Geological Survey.
Arkansas has suspended new wells near a fault line after 1,000 minor quakes were recorded. As for Ohio, officials say they'll keep the Youngstown, Ohio, well closed until they can be certain of the risks.