Distant seismic activity can trigger quakes at 'fracking' sites

Powerful earthquakes thousands of miles (km) away can trigger swarms of minor quakes near wastewater-injection wells like those used in oil and gas recovery, scientists reported , sometimes followed months later by quakes big enough to destroy buildings.

The discovery, published in the journal Science by one of the world's leading seismology labs, threatens to make hydraulic fracturing, or "fracking," which involves injecting fluid deep underground, even more controversial.

It comes as the U.S. Environmental Protection Agency conducts a study of the effects of fracking, particularly the disposal of wastewater, which could form the basis of regulations on oil and gas drilling.

Geologists have known for 50 years that injecting fluid underground can increase pressure on seismic faults and make them more likely to slip. The result is called an "induced" quake.

A recent surge in U.S. oil and gas production - much of it using vast amounts of water to crack open rocks and release natural gas, as in fracking, or to bring up oil and gas from standard wells - has been linked to an increase in small to moderate induced earthquakes in Oklahoma, Arkansas, Ohio, Texas and Colorado.

Now seismologists at Columbia University say they have identified three quakes - in Oklahoma, Colorado and Texas - that were triggered at injection-well sites by a major earthquake a long distance away.

"The fluids (in wastewater injection wells) are driving the faults to their tipping point," said Nicholas van der Elst of Columbia's Lamont-Doherty Earth Observatory in Palisades, New York, who led the study. It was funded by the National Science Foundation and the U.S. Geological Survey.

Fracking opponents' main concern is that it will release toxic chemicals into water supplies, said John Armstrong, a spokesman for New Yorkers Against Fracking, an advocacy group.

But "when you tell people the process is linked to earthquakes, the reaction is, 'what? They're doing something that can cause earthquakes?' This really should be a stark warning," he said.

Fracking proponents reacted cautiously to the study. "More fact-based research ... aimed at further reducing the very rare occurrence of seismicity associated with underground injection wells is welcomed, and will certainly help enable more responsible natural gas development," said Kathryn Klaber, chief executive of the Marcellus Shale Coalition.