They’ve been asleep since before the dinosaurs roamed Earth and now we’re waking them up.
Long-dormant, 300-million-year-old fault lines across Oklahoma are being “reawakened” by recent small earthquakes that have been previously linked to fracking, scientists reported in a new study out this week.
The faults could trigger much higher-magnitude and more destructive quakes than most of the smaller ones that have plagued the state in recent years, according to the new research.
Though not the central point of this study, previous research has identified hydraulic fracturing, or fracking, as a likely cause of the more than 3,600 small earthquakes that rattled central Oklahoma from 2009 through 2014. Fracking is a method of extracting natural gas and oil from rock that lies deep underground.
“By identifying the faults, we are providing some guidance about where major earthquakes can happen,” said Dan McNamara, a research geophysicist with the U.S. Geological Survey in Golden, Colo., and lead author of the new study.
The study findings will be used to develop a new earthquake-hazard map for Oklahoma that the geological survey is planning to issue later this year. It will mark the first time the state’s earthquake hazard maps will include suspected human-induced earthquakes.
Since late 2009, the rate of magnitude-3 or larger earthquakes in north-central Oklahoma has been nearly 300 times higher than in previous decades.
These reawakened faults in central Oklahoma could produce quakes as powerful as magnitude-5 and 6 earthquakes.
“Many faults are reactivating, with as many as 17 magnitude-4 earthquakes in 2014,” McNamara said. In 2011, one even reached magnitude-5.4 in strength near Prague, Okla.
“The work is fundamentally sound and done by several of the top people in the field,” said earthquake expert John Vidale, a seismologist from the University of Washington, who was not involved in the study.
“When one looks closely enough at the recent plague of earthquakes, they are on faults, and shallow enough to be plausibly affected by fluid injection (from the fracking process),” Vidale said.
The study has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.