Alexandra Witze reports that nearly 90 percent of temblors in the central U.S. are now caused by water injected into underground wells. Two new studies provide the strongest evidence yet that oil and gas companies have caused a rash of earthquakes in the central United States by injecting wastewater into underground wells.
One study, in Science, finds that the extraordinary increase in quakes took place almost exclusively within 15 kilometres of such wells. The second, in Science Advances, confirms that most seismic activity in one state, Oklahoma, is linked to wells that are used to dispose of huge volumes of saltwater.
Both findings are a significant step forward in explaining why earthquake rates have soared in the central United States. In the 1970s, there were no more than 30 magnitude-3 or greater earthquakes per year in the region. That rate accelerated sharply in 2009, reaching more than such 650 quakes last year.
Officials in the affected states, which include Oklahoma, Texas, Arkansas and Ohio, have been debating whether to strengthen regulation of these wells. In March, Kansas began requiring oil and gas operators in two counties that border Oklahoma to slash their injection rates.
The Science paper is the most definitive statistical analysis to link earthquakes and injection wells. Earlier research had analysed only single quakes or small groups of quakes. People had been focused on the smaller picture and not looking at the big picture, says team leader Matthew Weingarten, a graduate student at the University of Colorado at Boulder.
Aiming for that broader view, he and his colleagues assembled a database of more than 187,000 injection wells across the central and eastern United States, and compared that to data on 7,175 earthquakes that struck the region between 1973 and 2014. If an earthquake happened within 15 kilometres of an operating well, the researchers considered that quake and that well to be linked.
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