Does fracking cause earthquakes? MDN has covered various stories in the past on this topic. It seems likely that injection wells (not hydraulic fracturing, but the wastewater from fracking being injected deeply in disposal wells) in some locations have been tied to earthquakes in some areas. Notably, when injection wells in Arkansas stopped pumping pressurized liquids into the wells, earthquakes in the area all but stopped (see this MDN story). It certainly seems there is a cause and effect situation.
But what about fracking a single well? Is there a danger that fracking can cause earthquakes? Arthur McGarr, a geologist at the US Geological Survey in Menlo Park, California has worked out a formula for predicting how large an earthquake can result from pumping/injecting fluids underground, including fracking fluids. He recently presented his formula at the annual meeting of the American Geophysical Union in San Francisco, CA. McGarr subsequently spoke to the journal Nature about his formula:
“If you inject about 10,000 cubic metres, then the maximum sized earthquake would be about a magnitude 3.3,” says McGarr. Every time the volume of water doubles, the maximum magnitude of any quake rises by roughly 0.4. “The earthquakes may end up being much smaller, but you want to be prepared for the worst-case scenario,” says McGarr. The relationship is straightforward, but it is the first time that anyone has quantified it, he adds.*
For a frame of reference, 10,000 cubic metres is 2.6 million gallons. It takes at least that much to frack a shale gas well, sometimes double that volume. But not all of that liquid is forced down at once when fracking—it’s staged over time.
Perhaps most importantly, McGarr says his formula does not predict how likely an earthquake is to happen, that “depends on other factors, such as the strength and permeability of the rock.” Shale is a very strong, tightly-packed (low permeability) rock, meaning earthquakes from fracking are not at all likely to happen when drilling a single well.
*Nature (Dec 9, 2011) – Method predicts size of fracking earthquakes