Oklahoma felt seven small earthquakes over the weekend in just 14 hours, according to the U.S. Geological Survey.
The most severe registered at 4.3 on the Richter Scale. No injuries have been reported.
In June, Oklahoma surpassed California as the most earthquake-stricken state.
"The rate of earthquakes in Oklahoma has increased by about 50 percent since October 2013,” the USGS says.
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Austin Holland, a USGS research seismologist, told The Associated Press that scientists are still trying to determine if the earthquakes are natural or manmade.
One possible reason for the increase in earthquakes is hydraulic fracturing – fracking – which involves injecting chemically-treated waste water into deep layers of rock.
According to KRMG, one out of six Oklahomans gets a paycheck from the oil and gas business.
"Given the rate of earthquakes over the last six months, it's concerning enough to be worried about a larger, damaging earthquake happening,” USGS geophysicist Rob Williams told CNN.
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