Most people have become familiar with the complaints about how hydraulic fracturing, or fracking, is used extract oil or gas from shale: It contaminates local land and ground water, depletes local fresh water, potentially degrades local air quality, and could even trigger earthquakes.
There has only been anecdotal evidence of these concerns, until now: a new scientific study says it has linked earthquakes to fracking.
Research by Katie Keranen, an assistant professor of seismology at Cornell University in New York, found that injecting wastewater from fracking at underground disposal sites can cause earthquakes of moderate strength, or magnitude 3.
Keranen's research, published July 3 in the journal Science, backs up an earlier report by the U.S. Geological Survey (USGS) that found that some of the 450 earthquakes of magnitude 3 and larger in central and eastern parts of the United States between 2010 and 2013 coincided with the disposal of fracking wastewater.
The USGS report said Oklahoma, which has recently been experiencing twice as many moderate quakes as even quake-prone California has, provides a better understanding of how an increase in fluid pressure and the quick movement of wastewater over broad underground tracts can cause earthquakes.
It points to a study by the Oklahoma Geological Survey that Oklahoma County, which is close to a fault line, had only six earthquakes over eight years starting in 2000. Yet in 2009 there were 31, and in the subsequent 15 months, 850.
"It's been a real puzzle how low seismic activity level can suddenly explode to make (Oklahoma) more active than California," Keranen told USA Today.
Already, the findings by the U.S. and Oklahoma geological surveys have led some eastern and central states – already experiencing an increase in seismic activity -- like Colorado and Ohio to stop or suspend wastewater injections.
Fracking has been a valuable tool in extracting oil and gas from shale. The practice is credited with setting the United States on a course to become a net exporter of oil, and with making just one state, Texas, a rival for oil production to Iraq, OPEC's second-largest oil producer.
As a result, the oil industry is resisting further regulation of their practices, arguing that science already has demonstrated fracking's safety.
Energy in Depth (EID), a research association founded by the Independent Petroleum Association of America, posted a statement on its website decrying what it called recent "unmerited headlines" about fracking wastewater and earthquakes.
EID quoted Mark Zoback, a geophysicist at Stanford University, as saying that "microseismic events affect a very small volume of rock" and likened such tremors to "a gallon of milk falling off a kitchen counter."
It also quoted the U.S. National Research Council as saying that while wastewater injections do "pose some risk" of causing quakes, "very few events have been documented over several decades relative to the large number of disposal wells in operation."