Does Fracking Cause Earthquakes?

From Knovel.com:

New data suggest that the surge in oil and natural gas drilling throughout the U.S. is, in fact, spurring earthquakes.
Hydraulic fracturing, more commonly known as fracking, has become increasingly common throughout the U.S. The federal government has thus far allowed individual state legislatures to regulate the natural gas extraction method. States such as Pennsylvania and North Dakota have embraced fracking as a means of supporting economic growth, while other states, including New York, have instead studied whether to permit the practice.
Environmental and public health advocates have long questioned whether fracking imposes deleterious consequences on underground water supplies. However, over the past year or so, scientists have increasingly studied whether fracking could also potentially trigger minor earthquakes. There has been growing support for such engineering research from local municipalities where fracking is common, and the U.S. Geological Study recently conducted an overarching study on the matter, NPR reports.U.S. Geological Survey scientist Bill Ellsworth said that roughly a decade ago, researchers began to note that earthquakes were occurring in certain regions of the U.S. where they were not historically common. Earthquakes typically occur when faults in the Earth shift, colliding with one another and triggering such events. However, Ellsworth said that some earthquakes that have become increasingly common in the U.S. do not follow such an archetypal pattern.
"One thing we had begun to notice was that there were an unusual number of earthquakes in the middle of the country," Ellsworth told NPR.
At first, such earthquakes were relatively minor and infrequent, according to researchers. Still, they noticed that they became more common, particularly within the past three or so years.
"After that time, things really began to take off, and that's what really caught our attention," Ellsworth noted. "It is really quite surprising."
Underscoring how seismic activity in the middle of the U.S. has increased precipitously, Ellsworth said that scientists have logged a substantial rise in earthquakes since 2009, when there were 50 such events. He said that the number of earthquakes that struck the middle part of the continent in 2010 rose to more than 85, with that figure climbing to 134 in 2011.
Scientists are quick to assert that correlation does not necessarily prove causation, which is what prompted researchers to study whether there was a connection between an uptick in fracking in that region of the U.S. and the rise in earthquakes. Ellsworth and other seismologists, however, said that after carefully examining data, they are confident that the fracking industry is playing a major role in the increase in earthquakes.
However, fracking is only causing earthquakes in an indirect manner, according to the scientists' findings. Ellsworth and his colleagues said that fracking itself is not likely causing earthquakes, but, rather, the disposal of fracking wastewater is to blame. Oil and gas companies routinely inject wastewater derived from fracking into underground wells, and Ellsworth said such activity could be disruptive.
"We find no evidence that fracking is related to the occurrence of earthquakes that people are feeling. We think that it's more intimately connected to the wastewater disposal," he acknowledged.
Scientists said that because waste wells are often located even further underneath the ground than drilling wells, they are more likely to cause shifts in seismic activity. The shift in pressure around such wells – there are thousands of them scattered throughout the U.S. – is likely triggering the small, although still disruptive, earthquakes, according to the U.S. Geological Survey.











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