"We have been watching reports of earthquakes associated with fracking for the past few years. Until now they appeared to be mainly associated with injection of fracking waste fluids into deep disposal wells. That was serious enough, but at least there was the prospect of selecting disposal sites away from areas that are prone to seismic activity. Now there are credible reports of seismic activity directly related to the producing wells. This could be particularly troublesome to fracking shale in California."

 — Lou Allstadt, former Executive Vice President, Mobil Oil Corporation