Shaky Ground: For the last several years, increases in earthquake activity have led many to speculate that human activities such as deep well injection mining might be to blame.

DR first raised the issue in 2011, when we reported on a swarm of low-magnitude earthquakes that plagued Guy, Arkansas. The flurry of uncharacteristic quakes had some residents point to the practice of injecting drilling waste deep into the earth as the culprit.

While the area wasn’t normally prone to earthquakes, local geology made scientists wary of definitively connecting drilling with the quakes. Still, growing concern over the swarms led the Arkansas Oil and Gas Commission to not only shut down wastewater wells, but also ban the drilling of any new disposal wells.

As time went on, similar events across the country continued to point to the possibility that injection wells could spawn manmade earthquakes. Subsequent studies in Oklahoma, Arkansas, Ohio, Colorado, and internationally have shown links between the two.

Standing Firm: More recently, additional evidence has surfaced to support those connections. A January news report from the U.S. Geological Survey, for instance, announced that the number of U.S. earthquakes had increased dramatically in the past four years—and that in some instances increases coincided with deep well injections.

USGS scientists logged an average of more than 100 magnitude 3.0 or larger quakes per year since 2010. That compares with the previous average of 20 quakes per year for the years from 1970-2010. In a variety of locations, such as rural Oklahoma, where a 5.6 quake in 2011 caused injuries and damage, geologists have been able to show a strong correlation between seismic activity and wastewater injection.

“Injection-induced earthquakes, such as those that struck in 2011, clearly contribute to the seismic hazard,” USGS geophysicist William Ellsworth writes in the abstract of a Science article on the subject. But he adds, “Quantifying their contribution presents difficult challenges that will require new research…”

Digging Deeper: The USGS is partnering with other agencies, including the Environmental Protection Agency and the Department of Energy, to better understand how wastewater injection contributes to seismicity. Meanwhile, Ellsworth suggests developing a “threshold system” where changing seismicity could be monitored and wastewater disposal halted when the threshold was reached.

Although the system would help mitigate the risk of damaging quakes, Ellsworth noted that current reporting of wastewater injection rates and other factors would need to increase. That could mean pushback from the oil and gas industry, but even industry-friendly states such as Colorado and Kansas are looking at ways to limit quake risks.

“Recent seismic activity in south-central Kansas has raised concerns that fluid injection might be related,” Kansas Gov. Sam Brownback said Monday as he announced a state task force to study the issue. “This is a matter of public safety.”