5.7 quake tied to wastewater injection

Columbia University researchers say a 5.7 magnitude quake in Oklahoma in 2011 may be the largest ever linked to the injection of wastewater into the ground.

The temblor, the biggest ever recorded in Oklahoma, destroyed 14 homes, buckled a highway and left two people injured.

Scientists have linked a rising number of quakes in normally calm parts of Arkansas, Texas, Ohio and Colorado to below-ground injection of wastewater, used both in hydrofracking to crack open rocks to release natural gas and in coaxing petroleum out of conventional oil wells, a Columbia release said Tuesday.

In both processes, brine and chemical-laced water has to be disposed of, often by injecting it back underground elsewhere, where it has the potential to trigger earthquakes.

The water linked to the 2011 Oklahoma quake was a byproduct of oil extraction at one set of oil wells and was pumped into another set of depleted oil wells targeted for waste storage, Columbia researchers said.

The scientist said they believed as wastewater replenished compartments once filled with oil, the pressure to keep the fluid going down had to be increased, to the point where a known earthquake fault jumped.

"When you overpressure the fault, you reduce the stress that's pinning the fault into place and that's when earthquakes happen," study coauthor Heather Savage, a geophysicist at Columbia's Lamont-Doherty Earth Observatory, said.

The study suggests "the risk of humans inducing large earthquakes from even small injection activities is probably higher" than previously thought, study co-author Geoffrey Abers said.