More on Earthquakes and their relation to Fracking.

Powerful earthquakes thousands of kilometres away can trigger swarms of minor quakes near fracking wells , scientists have reported.

They also report these earthquakes were 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.

“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 US Geological Survey.

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 an “induced” quake.

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

Fracking opponents’ main concern so far is that fracking 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.

The largest fracking-induced earthquake “was magnitude 3.6, which is too small to pose a serious risk,” he wrote in Science.

But van der Elst and colleagues found evidence that injection wells can set the stage for more dangerous quakes.

Because pressure from wastewater wells stresses nearby faults, if seismic waves speeding across Earth’s surface hit the fault it can rupture and, months later, produce an earthquake stronger than magnitude 5.

What seems to happen is that wastewater injection leaves local faults “critically loaded,” or on the verge of rupture.

http://www.stuff.co.nz/science/8924110/Distant-quakes-rattle-fracking-sites