Earthquake outbreak in central US tied to drilling wastewater

A spate of earthquakes across the middle of the U.S. is “almost certainly” manmade, and may coincide with wastewater from oil or gas drilling injected into the ground, U.S. government scientists said in a new study. Researchers from the U.S. Geological Survey said that for the three decades until 2000, seismic events averaged 21 a year in a central U.S. region. They jumped to 50 in 2009, 87 in 2010 and 134 in 2011. Those statistics, included in the abstract of a research paper to be discussed at the Seismological Society of America conference next week in San Diego, were released a month after Ohio officials concluded that earthquakes there last year probably were caused by wastewater from hydraulic fracturing for natural gas injected into a disposal well, a state report said in March. “Our scientists cite a series of examples for which an uptick in seismic activity is observed in areas where the disposal of wastewater through deep-well injection increased significantly,” David Hayes, the deputy secretary of the U.S. Department of Interior, said in a blog post yesterday, describing research by scientists at the U.S. Geological Survey. The earthquakes were “fairly small,” and rarely caused damage, Hayes said. He said not all wastewater disposal wells induce earthquakes, and there is no way of knowing if a disposal well will cause an earthquake, he wrote. In hydraulic fracturing -- or fracking -- water, sand and chemicals are injected into deep shale formations to break apart underground rock and free natural gas trapped deep underground. Much of that water comes back up to the surface and must then be disposed of. An abstract of the federal study, which was led by William Ellsworth, Earthquake Science Center staff director for the U.S. Geological Survey in Menlo Park, California, was published online earlier this month. A full version of the study wasn’t immediately available. The area studied included parts or all of states including Ohio, Colorado and Oklahoma, the study said. “A naturally-occurring rate change of this magnitude is unprecedented outside of volcanic settings or in the absence of a main shock, of which there were neither in this region,” Ellsworth and his colleagues wrote.