Wastewater cap could dunk Oklahoma quake risk

New wastewater disposal regulations in Oklahoma will be enough to steady the state’s shaky ground, new research predicts.

The injection of wastewater from oil and gas operations into underground wells has caused Oklahoma’s seismic activity to skyrocket (SN: 8/9/14, p. 13). In response, state regulators earlier this year ordered a 40 percent reduction in the volume of water pumped underground. After studying the statistical link between wastewater disposal and earthquakes, Stanford University geophysicists Cornelius Langenbruch and Mark Zoback predict that seismic activity in the region will return to historically normal levels within the next few years.

“It should be possible to dispose a limited volume of wastewater underground without inducing any earthquakes,” Langenbruch says. The same process can help reduce the seismic hazard in other earthquake-prone areas as well, the researchers report online November 30 in Science Advances.

Oklahoma’s recent gas and oil boom has led to billions of liters of water left over from the extraction process being stashed away each month deep underground. The pressure of that water can unclamp seismic faults, causing earthquakes (SN: 7/11/15, p. 10). As a result, around 900 earthquakes registering magnitude 3 or stronger rattled north-central Oklahoma in 2015, compared with about one per year statewide before 2009.

Modest amounts of wastewater injection won’t trigger much seismic activity, Langenbruch and Zoback found by comparing injection rates and seismic activity from 2008 to early 2015. But if injection rates cross a certain threshold, the number and strength of induced quakes soars. In Central Oklahoma, for instance, sporadic induced earthquakes started in 2009 after wastewater injection rates exceeded about 3.6 billion liters per month.

Keeping rates below such thresholds is key to reducing the region’s risk of damaging earthquakes, Langenbruch says, although “the best thing in terms of seismic hazard would be to stop injecting wastewater at all in Oklahoma.” Seismic activity in Oklahoma, he points out, has already dropped off significantly compared with last year.

Factors other than regulation probably contributed to that decline, says Rick Aster, a seismologist at Colorado State University in Fort Collins. The recent fall in oil prices and resulting drop in oil production also may have played a role, he says. “We’re not sure that regulation is the only knob being turned.”