Waste water from oil and gas drilling that was pumped underground may have set off a magnitude-5.7 earthquake in the central United States.

In November 2011, a series of quakes near Prague, Oklahoma, could be felt across 17 states. A team led by Katie Keranan at the University of Oklahoma in Norman analysed the aftershocks to see how faults ruptured. Of three segments to break in the fault network, the first was located within 200 metres of a shaft that had been used to inject fluid underground for 18 years. The authors conclude that changes in ground stress as the fluid built up probably caused the faults to fail.

Wastewater injections are known to have triggered earthquakes before, but this is the largest that has been tied to the practice so far, the authors say. They suggest that even a relatively small volume of fluid can lead to significant quakes many years down the line.

Geology http://dx.doi.org/10.1130/G34045.1 (2013)