BOULDER, Colo., June 18 (UPI) -- Fracking-induced earthquakes are on the rise through the middle of the United States. And injection wells aren't just responsible for small rumbles -- hydraulic fracturing has been blamed for several large quakes in recent years.
According to new research by scientists with the University of Colorado Boulder and the U.S. Geological Survey, between 2011 and 2012, high-rate injection wells were associated with earthquakes ranging in magnitude from 4.7 to 5.6. The most serious rumbles were measured in Prague, Oklahoma; Trinidad, Colorado; Timpson, Texas; and Guy, Arkansas.
"This is the first study to look at correlations between injection wells and earthquakes on a broad, nearly national scale," study leader Matthew Weingarten, a researcher at Boulder's geological sciences department, said in a press release. "We saw an enormous increase in earthquakes associated with these high-rate injection wells, especially since 2009, and we think the evidence is convincing that the earthquakes we are seeing near injection sites are induced by oil and gas activity."
Researchers compared earthquake data with injection well activity throughout the middle of the country, analyzing high-rate wells -- those that pump more than 300,000 barrels of wastewater into the ground each month -- from Colorado to the Eastern Seaboard.
Of the more than 180,000 wells studied, 18,000 were found to be associated with an uptick in local seismicity. Though some two-thirds of these wells were oil recovery wells, wells used for wastewater disposal were 1.5 times as likely to be associated with earthquakes.
"Oil recovery wells involve an input of fluid to 'sweep' oil toward a second well for removal, while wastewater injection wells only put fluid into the system, producing a larger pressure change in the reservoir," said Shemin Ge, a geological sciences professor at Boulder.
Many injection wells have been around for decades, without associated increases in seismicity. But researchers say newer wells, with higher intensity injection rates (even if short-lived), are more capable of influencing local fault lines.
"It's really the wells that have been operating for a relatively short period of time and injecting fluids at high rates that are strongly associated with earthquakes," said Weingarten.
As researchers point out, some areas are simply more vulnerable to seismic influence of injection wells. Wells in these areas may need to be more closely monitored and strictly regulated.
The new research was published in the journal Science.