John Armbruster, a seismologist at Columbia University, said the 11 earthquakes in eastern Ohio around Youngstown exhibited a pattern and power not normal for the region or for natural quakes, the Pittsburgh Tribune-Review reported Tuesday.
The earthquakes have been getting larger over several months in an area where that type of regular seismic activity isn't common, Armbruster said.
"Things look different than they did before," he said. "It's not absolute proof, but it seems the doubt in my mind is small based on my 40 years' experience studying earthquakes."
A 4.0 quake Saturday hit 5 miles northwest of Youngstown just one day after the Ohio Department of Natural Resources halted operations at a deep-injection disposal well less than 3 miles away.
The department put a moratorium on four other disposal wells about to open nearby.
"The way we're looking at it, there's enough correlation," Andy Ware, the department's deputy director, said, noting the depth of the Saturday quake was closer to the well bottom than previous quakes had been.
"Putting all that together, we think it's reasonable to halt all future injections within a 5-mile radius until we have a better understanding of what may be causing the seismic activity."
Fluid disposal increased in Ohio in 2011 as Pennsylvania gas drillers were shipping more wastewater across the border, Ohio officials said.
Ohio has 177 injection wells compared with six in Pennsylvania, where there isn't as much cheap, permeable and available space underground, the Tribune-Review reported.