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There are plenty of reasons to worry about fracking-groundwater contamination, methane leaks, that flaming tap water thing. But can it really cause earthquakes? That’s the question the US Geological Survey set out to answer after a spate of tremors in the Midwest-an area not usually known for earthquakes-alerted scientists to the possibility that some of them might be man-made.
Seismic activity in the Midwest started increasing around 12 years ago but picked up significantly in the past few years, says seismologist Bill Ellsworth, the lead author of a new USGS study examining potential links between fracking and earthquakes in the region. Since 1970, the baseline for earthquakes in the Midwest measuring above a 3.0 hovered at around 21 per year, but beginning in 2001, that number began to rise. There’s been a “remarkable increase” in the past few years: The number of 3.0-plus earthquakes rose from 29 in 2008 to 50 in 2009, then to 87 in 2010, and in 2011 to a staggering 134. Something unusual was going on, but what? As Ellsworth and his colleagues at USGS ask in the study, “Is this increase natural or manmade?” And if it’s man-made, is fracking-which has ramped up in the region in the past several years-to blame?
According to the study, the answer to the first question is “almost certainly.” But the second one is a little more complicated. Though fracking does cause tiny tremors, the USGS scientists found no links between the process of fracking itself and the larger earthquakes that have been occurring more frequently. They did, however, notice that earthquakes have clustered around wastewater wells in Oklahoma, Arkansas, and neighboring states. Disposing of wastewater by pumping it deep into the ground is standard practice in many industries, including mining, chemical manufacturing, and oil and gas extraction, and the oil and gas industry alone operates tens of thousands of wastewater disposal wells. But the recent surge of fracking activity, which uses millions of gallons of water to crack rock deep in the ground and release natural gas, has boosted the volume of wastewater being injected into the ground.