Wednesday, January 11, 2012

Man Made Earthquakes

San Andreas fault- Wikimedia
The recent concern about the potential of inducing earthquakes by fracking (hydraulic fracturing in the mining of natural gas) shouldn't come as a surprise.  A story on npr.org explains that earthquakes have been tied to human activities for years.

According to Wikipedia, "Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests."  These even have their own name, induced seismicity.

Most of these induced seismic events are relatively small.  A major exception comes from the creation of large reservoirs with dams in excess of 300 feet tall.  The mass of water where there was none before is compounded by water which is forced into rock fissures, essentially lubricating the fault so it slides easier.  


The 6.3 magnitude Koynangar earthquake in India killed 180 people.  The epicenter, fore and aftershocks all were located around the Koyna Dam reservoir.  Another example is the seismic shocks recorded during the initial water filling behind the Vajont Dam in Italy in 1963.  A subsequent landslide almost filled the reservoir and massive flooding caused around 2000 deaths.  After the reservoir was drained, the seismic activity essentially quit.


Although both the extraction of fossil fuel and hydraulic fracturing on natural gas wells have triggered earthquakes, the scale has been small thus far.  The experience with dams has taught us the importance of geologic studies to assess the risk.

The USGS Earthquake Hazards page has up to date information on earthquakes around the US.  You can even get real-time earthquake reports by iGoogle and Twitter.  These reports may not match your average tweets from Charlie Sheen but they will be more earthshaking.

Note:
On a happier note, the eurekalert.org reports that the Energy Institute at the University of Texas at Austin found no evidence of ground water contamination related to hydraulic fracking.  All contamination has been due to faulty equipment and procedures common to all drilling for oil, natural gas, etc. 

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