(NaturalNews) Injection wells used to dispose of wastewater from oil and gas drilling are causing earthquakes that may place public safety at risk, researchers are increasingly warning.
Most recently, in a study published in the journal Science on July 3, researchers from Cornell University concluded that the recent dramatic increase in central Oklahoma earthquakes is probably due to just a few wastewater injection wells.
"Our results, using seismology and hydrogeology, show a strong link between a small number of wells and earthquakes migrating up to 50 kilometers [30 miles] away," lead researcher Katie Keranen said.
Quakes up to 20 miles away
In recent years, new technologies and a decreasing availability of the highest quality oil and gas has made formerly marginal drilling techniques profitable. This has led to a boom in shale mining across North America, including the controversial technique of hydraulic fracturing, or "fracking."
Fracking consists of injecting a mix of chemicals, water and sand underground to crack open rock and enable oil and gas drilling. The water must then be pumped out, but at that point has been contaminated not just with the chemicals used in the mining process but also with salt and even radiation. In order to dispose of this wastewater, oil and gas companies have taken to injecting it thousands of feet into the ground, sometimes into tapped out oil and gas wells. According to the Environmental Protection Agency, there are now 144,000 wastewater injection wells in the United States, collectively receiving more than 2 billion gallons of wastewater per day.
Scientists have raised concerns that injecting such a large volume of fluid into the earth's crust may be increasing the pressure on fault lines and thereby altering seismic patterns. According to the U.S. Geological Survey (USGS), the number of earthquakes above 3.0 magnitude has jumped from an average of 21 per year from 1967 to 2000, to an average of 100 per year between 2010 and 2012.
Nearly all these quakes occurred in states with wastewater injection. Between 2008 and 2013, Oklahoma earthquakes accounted for nearly half of all seismicity in the central and eastern United States combined.
The new study looked specifically at the Jones earthquake swarm, or a cluster of quakes centered near Oklahoma City since 2008. The researchers confirmed that high-volume injection wells were, in fact, triggering earthquakes, and much farther away than had previously been thought possible -- up to 30 km (20 miles) from a well, rather than the 5 km previously assumed.
They found that four of the highest-volume wells were capable of triggering one-fifth of all recent central U.S. earthquakes, in a total area of almost 2,000 square kilometers (800 square miles).
More troublingly, they found that continued use of the same wells has actually been increasing the range over which those wells can induce earthquakes, through ever-increasing subterranean pressure. This also increases the risk that these wells will trigger higher-magnitude quakes.
Wastewater-injection-induced earthquakes have become enough of a concern that the recent annual meeting of the Seismological Society of America in May featured a special session to discuss the issue. One problem is that wastewater injection renders previous estimates of seismic risk unreliable. This may threaten public safety in areas where dams, nuclear power plants or other high-risk infrastructure was constructed presuming lower levels of seismic risk.
A paper presented at the meeting found that, of all factor considered, wastewater injection was the most likely culprit behind the surge in Oklahoma and Texas earthquakes.
"From the results of this study, the total volume of injected fluid seems to be the factor that limits the magnitude, whereas the injection rate controls the frequency of earthquake occurrence," USGS researcher Art McGarr said.