One of the side-effects of the extraction of natural gas by hydraulic fracture, widely known as fracking, is the possibility that the injection of water into gas-bearing rocks will cause earthquakes. There is no doubt that this can happen, but as summarized in a recent paper by William Ellsworth of the U.S. Geological Survey’s Earthquake Science Center, the earthquakes from these oil and gas wells are too small to pose a significant hazard. Most are below magnitude 2.0, which can barely be sensed by humans.
More worrisome are earthquakes that are induced by the disposal of waste-waters that return to the surface during gas production. Oil and gas companies like to dispose of these waters deep underground, because they often contain hazardous concentrations of substances that are difficult to remove by standard wastewater treatment. Sometimes large volumes of water are injected in waste-disposal wells, which can activate existing faults in the underlying rock.
The frequency of earthquakes of a magnitude greater than 3.0 has increased markedly in the U.S. over the past five years, perhaps associated with a greater number of waste-water disposal wells. Nearly 200 small earthquakes were recorded in 2011, at least some from human activities.
Clearly, we need a seismic monitoring and regulatory network in place if the pace of hydraulic fracture and disposal of its waste waters continues to expand.
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Web Links
Ellsworth, W.L. 2013. Injection-induced earthquakes. Science, July 12, p. 142.
Photo, taken on August 1, 2011, courtesy of the U.S. Army Corps of Engineers via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.