Scientists Can Now Tell the Difference Between Natural and Man-Made Earthquakes

December 17, 2015 | Joanne Kennell

Quake damage to River Road
Photo credit: Martin Luff/Flickr (CC BY-SA 2.0)

Earthquakes triggered by fracking increase in magnitude over time.

If you don’t believe hydraulic fracturing, also known as “fracking,” causes earthquakes, I dare you to tell that to residents in Oklahoma, Texas, Ohio and even British Columbia, Canada — where fracking-related earthquakes have been rising dramatically.  Fracking is the process of injecting fluid at a high pressure into rocks, to force open existing cracks and extract oil or gas.

To end the debate of whether fracking does or does not cause earthquakes, researchers from Stanford University have developed a technique that can help scientists distinguish between natural and manmade earthquakes.  It turns out that earthquakes triggered by human activity follow indicative patterns.

Assistant professor of geophysics, Jenny Suckale, at Stanford’s School of Earth, Energy and Environmental Sciences, as well as postdoctoral researcher David Dempsey, analyzed a sequence of earthquakes near the town of Guy, Arkansas, from 2010 to 2011.

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Scientists suspected that the Arkansas earthquakes were triggered by the injection of approximately 94.5 million gallons of fracking wastewater into to nearby wells, which then made its way into the basement layer during a nine-month period.  The term “basement” refers to the rock located beneath a sedimentary rock cover that may contain oil and gas reserves.  This addition of water in the basement layer adds more stress to already stressed faults, until one eventually slips and releases seismic waves, resulting in an earthquake.

Alarmingly, one of the study’s main conclusions is that the likelihood of large-magnitude manmade or “induced” earthquakes increases over time.  A model simulation performed by Suckale and Dempsey found a linear relationship between frequency and magnitude of induced earthquakes, with magnitudes increasing the longer wastewater is pumped into a well.

“It's an indication that even if the number of earthquakes you experience each month is not changing, as you go further along in time you should expect to see larger magnitude events,” said Dempsey.

However, the trend does not continue indefinitely.  The study showed that the magnitude of manmade quakes begin to fall after reaching some maximum intensity, but how large is that limit?  “Does it taper off at magnitude 3 or a more dangerous magnitude 6.5?” Suckale said.

Previous studies had found that the rate of wastewater injection was more important for triggering earthquakes, rather than total volume.  However, the Stanford study found that, given similar injection rates, there was a direct relationship between volume and the occurrence of earthquakes.  For example, of the two wells studied near Guy, Well 1 received four times the wastewater as Well 5, and triggered four times as many earthquakes.

The results could have significant impacts on the oil and natural gas industry, as well as for government regulators.  Currently, if a high-magnitude earthquake occurs, fracking activities shut down.  However, according to Suckale, a better approach might be to limit production before a large quake occurs.

I think we can all agree that something needs to be done.

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