(OKLAHOMA CITY) -- For the first time ever, on Monday the United States Geological Survey issued an earthquake advisory for a state east of the Rocky Mountains, Oklahoma.
The USGS said on Monday that the risk of an earthquake of magnitude greater than 5.0 has noticeably increased in central Oklahoma. Robert Williams, a geophysicist with the USGS, said that the agency can't predict when or where the state's next earthquake might take place.
"This is an advisory based on the increase in earthquake rate over the last five years, and especially the last six months," Williams told ABC News.
On a per-mile basis, there have been almost as many tremors in Oklahoma as there have been in California this year, Williams said. He added that the increased risk may be related to fracking activity, saying that "the contributing factor may be related to injection and cycling of fluid at the subsurface, associated with oil and gas activity in central and north-central Oklahoma.
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