“It’s true that you can’t have an earthquake larger than a given fault can provide,” said Serge Shapiro, a professor at the Free University of Berlin who has studied what scientists refer to as induced seismicity. “But an earthquake even of magnitude 4 in a populated area can be an unpleasant thing.”

Officials with D & L Energy, the Youngstown company that has been disposing of the waste, and with the Ohio government say there is no proof of a link between the disposal well and the earthquakes. “Right now we can’t definitively say yes or no,” said Tom Tugend, deputy chief of the gas and oil division of the Ohio Department of Natural Resources. But the state has asked the company to plug the bottom 250 feet of the well with cement as a precaution, to ensure that it is sealed from the deeper rock where the earthquakes are thought to have occurred.

Image Credit... The New York Times

State officials are also working with researchers from the Lamont-Doherty Earth Observatory, a part of Columbia University, who have installed four temporary seismometers within several miles of the well. If more earthquakes occur, the instruments will help determine location and depth more precisely. “It should help us make the case one way or another — is this related or not,” said John Armbruster, a Lamont seismologist.

C. Jeffrey Eshelman, a spokesman for the Independent Petroleum Association of America, said that as far as the industry was concerned, “it has been impossible to determine whether hydraulic fracturing has anything to do with” the quakes like those in Ohio.

“But it’s in our best interest to understand what’s going on,” he said. “Although they are minor incidents, they are still something to be taken seriously.”

Scientists say that although it is known that wells — and reservoirs and quarries, among other things — can induce earthquakes, it can be difficult to prove a connection because there is not enough data. So specific cases often become a subject of debate.