Natural gas extraction techniques vary, but fracking, or hydraulic fracturing, has been linked to water pollution, methane emissions, and even increased seismic activity [read: Earthquakes].

Fracking has turned out to be very controversial. Fracking is an extraction process that involved injecting pressurized fluids into the shale layer of stone containing natural gas or petroleum. The fluids fracture the shale, leaving behind small cracks, which are kept open by sand or some other material that allows natural gas to propagate back to the well where it can be contained [mostly] and shipped to refineries.

If you think about it, injecting liquid into an otherwise “dry” layer of stone should have other effects, such as allowing the layers to slip against each other. [Think: WD-40] In geological terms, we refer to this as an earthquake. Along fault lines, earthquakes occur with regularity, but in areas where natural gas has been found, there are no fault lines, and earthquakes are rare to nonexistent.

The rise in earthquake activity surrounding zones where fracking is being undertaken on a grand scale was never fully linked to fracking itself, until now. Scientists already know that naturally-occurring subsurface fluid can make an area prone to earthquakes, so what happens when human beings put it there, but the same thing?

After looking at the data from three major earthquakes in 2011 and 2012, scientists determined that they caused smaller earthquakes in the Mid-West US. These earthquakes didn’t occur in the US or even the North American Continent, but thousands of miles away. For example, the March 11, 2011, 9/0-magnitude, Tohoku-Oki earthquake, off the coast of Japan, is more than 6,000mi from related aftershocks in Prague, Oklahoma.

Image © MotherJones.com