Scientists have linked the underground injection of oil-drilling wastewater to a magnitude-5.7 earthquake in 2011 that struck the US state of Oklahoma. Wastewater injection from drilling operations has been linked to seismic events in the past, but these have typically been much smaller quakes.
They also have tended to occur in the first weeks or months of injection. The study in Geology suggests that "induced seismicity" can occur years after wastewater injection begins.
Wastewater was first injected into Oklahoma's Wilzetta oilfields, near the town of Prague, some 18 years prior to the November 2011 series of quakes that included three of magnitude 5 or greater.
The new study adds to an increasing body of evidence that the injection of wastewater is correlated to an increase in seismic events. A comprehensive review in 2012 by the US' National Academy of Sciences found that "injection for disposal of waste water derived from energy technologies into the subsurface does pose some risk for induced seismicity".