Andreas Späth

Does fracking cause earthquakes or not?

2013-07-23 07:36

Andreas Späth

Last week I asked (and tried to answer) the question whether or not fracking causes groundwater pollution. Another issue that's been in the news lately and one that causes a fair amount of confusion concerns the connection between the controversial oil and gas extraction method and earthquakes.

On one level, the answer to this one is straight forward enough: yes, fracking does cause earthquakes. In simplistic terms, the pressurised fluids injected into fracking wells lubricate pre-existing but dormant fault planes and thus increase the likelihood that they rupture, causing two adjoining bodies of rock to slide and grind past each other and the ground above to shake.

But that only addresses part of the matter. The more pertinent concern is how severe these fracking-related seismic events are.

In 2011, the British Geological Survey confirmed that two earth tremors near Blackpool in North-West England were most likely to have been the result of exploratory shale gas drilling operations employing fracking in the area and the company doing the drilling, Cuadrilla Resources, accepted responsibility for the events.

Causing earthquakes

The quakes in question were very weak, however, with magnitudes of 2.3 and 1.5 on the Richter scale respectively, and they caused neither damage nor injuries.

A recent study by a group of British scientists identified merely three earthquakes caused by human activity that could be attributed to fracking since 1929 - one each in the USA, Canada and the UK. The largest of these occurred in the Horn River Basin in Canada and had a magnitude of 3.8.

While the study "established beyond doubt" that fracking can indeed cause earthquakes, the lead author, Professor Richard Davies of Durham University concluded that it's not a significant mechanism for inducing tremors that can actually be felt by anyone other than a seismologist using fairly sensitive measuring equipment.

So if fracking is ever going to happen in South Africa, a direct increase in earthquakes powerful enough to cause damage or injury is not something we should worry about a whole lot. Which is, of course, not the same as saying that fracking won’t cause damage and injury in a number of other ways - it will!

But this is not quite the end of the story. While fracking itself is not a major inducer of dangerous earthquakes, a closely associated activity may well be.

Fracking produces millions of litres of wastewater in the USA every year and a lot of that waste is disposed of by pumping it into deep underground wells. Over 150 000 of these injection wells are now in operation in the country to get rid of wastewater from the oil and gas fracking operations.

This practice (which is illegal in the EU) has been directly linked to significantly more severe earthquakes than those caused by fracking itself. In 2011, for example, a 5.7 magnitude tremor in Oklahoma believed to be caused by injection wells for fracking wastewater was felt in 17 states, destroyed 14 homes and injured two people.

In Arkansas, earthquakes of magnitude 2.5 and larger have increased drastically since similar injection wells became operational in 2009 (up from just one in 2007 to 157 in 2011) and 98% of them occurred within 6 kilometres of three wells after wastewater injection started.

The verdict

In the whole of the American Midwest, in what should naturally be a tectonically stable region, "a remarkable increase" in the rate of earthquakes of magnitude 3 and higher has been documented since the fracking boom took off there.

This month, researchers showed that in areas that have undergone extensive underground injection of fluids, significantly tremors can be triggered by much larger earthquakes thousands of kilometres away. The event in Oklahoma I mentioned above, for instance, is likely to have been set off by a magnitude 8.8 quake in Chile.

So what's the verdict in a nutshell?

Current scientific opinion suggests that fracking in and of itself is unlikely to cause dangerous earthquakes. If, however, large quantities of wastewater from fracking operations are injected into disposal wells, the area in question is likely to become susceptible to more powerful and potentially damaging earthquakes.

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath
 
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