Oklahoma’s largest recorded earthquake, a 5.7-magnitude quake in 2011 that was felt for hundreds of miles, was probably caused by fluid injection at drilling sites, a team of university and federal scientists has concluded.
The scientists said they found “conclusive” evidence that the earthquake near Prague, Okla., was caused by years of wastewater injections at the drilling site, which lies along a fault line.
“Significantly, this case indicates that decades-long lags between the commencement of fluid injection and the onset of induced earthquakes are possible,” the authors wrote in the study abstract.
The study by seismologists from University of Oklahoma, Columbia University and the U.S. Geological Survey came out Tuesday in the science journal Geology.
“We have a lot of evidence that certainly leads us to believe” the quake was caused by the injections, said co-author Elizabeth Cochrane, according to the Associated Press.
These injections are not related to fracking, in which water, chemicals and sand are injected deep underground to extract gas and oil trapped in shale formations.
Oklahoma’s state seismologist disagreed with the study’s assessment. The Oklahoma Geological Survey said on Friday that evidence from the quake, the drilling site and other similar events don’t back up the claim that pressure from fluid injections caused the quake.“The interpretation that best fits current data is that the Prague Earthquake Sequence was the result of natural causes,” OGS said. The Prauge earthquake and other seismic activity “would benefit from further study,” OGS said