No fracking earthquakes

November 11, 2011 in Earthquakes

On February 28th 2011, a 4.7 magnitude earthquake struck Central Arkansas.  A few months later, The Arkansas Oil and Gas Commission imposed a moratorium on natural gas disposal wells over fears that the drilling and the earthquake was connected.  Recent earthquakes in Oklahoma have raised similar concerns as a whole new battleground has opened up in the fight over fracking.

Let’s just get one thing out of the way: Earthquakes occur when rocks break.  Hydraulic fracturing, or fracking, breaks rocks (it’s right there in the title).  Therefore, fracking causes earthquakes.

Before we get ahead of ourselves, let me also add that everything we do, from walking to driving and yes, even bicycling, releases minute amounts of seismic energy detectable by a seismometer that is sufficiently close by.

The point is that “causing an earthquake” is not really a problem if the earthquake is small.  Oklahoma’s own Geological Survey released a study suggesting that fracking may be responsible for a recent swarm of quakes, although none measured greater than 2.8 on the Richter Scale.  A similar conclusion was reached following a small series of earthquakes in Britain, again with no structural damage.

If fracking can cause a 2.8 magnitude earthquake, why not a 5.6?  It’s only twice as big, right?  Wrong.

The two numbers don’t sound that far apart, but they are.  The reality is that a 5.6 earthquake is over 16,000 times as powerful as a 2.8.  In other words, they simply are not in the same league.

Lost in all of this is a proper explanation of exactly how fracking is related to earthquakes at all.  This post is not going to tell you if the Oklahoma, Virginia, or any other quake was caused by fracking (see here for more).  This post is about HOW fracking COULD cause earthquakes IF they cause them at all.  Ready?

 

Potential way fracking COULD cause earthquakes #1: Breaking rocks

The entire purpose of hydraulic fracturing is to open small cracks deep in the ground that allow natural gas to flow to the drill hole where it is pumped to the surface.

This is the simplest and most direct way that fracking releases seismic energy, however almost no one is suggesting that these small cracks are causing the earthquakes in Oklahoma.  To explain, we need to do some math.

 

 

That wasn’t so bad, was it?  Large earthquakes occur along large faults, which are many kilometers long.  Fracking breaks rocks, but the cracks are very small.  Therefore, they cannot release that much energy.

 

Potential way fracking COULD cause earthquakes #2: Lubricating faults

When people suggest that fracking causes earthquakes, this is generally what they mean.  Fracking requires LOTS of water and when it returns to the surface, it’s filled with harmful chemicals and radioactive elements.  This water is often disposed of by injecting it into deep rock formations where it cannot contaminate drinking water (that’s the theory, at least).  The ground under Oklahoma, Virginia, and the rest of the United States is filled with ancient faults that are constantly under stress.  The only reason they aren’t sliding around all the time is that there is a lot of friction that holds them back.  Injecting water into these faults can reduce friction and allow them to move, causing earthquakes.


 

In this scenario, the faults are already under stress and the water simply lubricates them enough to move.  There is precedent for this.  In 1963, a landslide at the Vajont Dam in Italy killed 2000 people, a disaster partially blamed on rain water lubricating existing faults.  However, it’s important to remember that the study by the Oklahoma Geological Survey suggests that these quakes are small and occur close to the well.

To wrap all this up, fracking CAN trigger earthquakes but there is no evidence that they could trigger LARGE earthquakes.

Got a question about earthquakes?  Just leave a comment.

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