California is known for its earthquakes, but now Oklahoma and Kansas have the same risk levels, according to USGS forecasts of human-caused quakes. Many are concerned that it may be related to mining for oil through hydraulic fracturing.
An annual seismic hazard forecast released Wednesday claims that the risks posed by human-induced tremors are increasing in Kansas and Oklahoma. In 2016, Oklahoma had the highest risk of earthquake-related damage and in September experienced the largest shock in the state to date.
The report from US Geological Survey (USGS) scientists predicted that while the strength of temblors was increasing in Oklahoma, the overall number of earthquakes was predicted to decrease. In fact, the number has been on a steady decline since 2015, the Oklahoman reported.
However, that is not necessarily cause for celebration.
“While we have seen a strong drop in frequency, it would not be totally out of the question to see another moderately large earthquake,” Jeremy Boak, director of the Oklahoma Geological Survey, told the Oklahoman. “However, we expect the rate to continue to fall before it flattens out.”
Typically the strength of earthquakes will decrease along with their frequency, but that has not held true for Oklahoma. Last year, the state experienced its two strongest tremors with a 5.8 magnitude in September near Pawnee, followed by a 5.3 magnitude near Cushing in November.
The numbers in overall earthquakes also decreased in 2016 for Oklahoma where until 2000, there were only two seismic events above a 2.7 magnitude. In 2014, that number reached 2,500 and by 2015, grew to 3,500, the Los Angeles Times reported.
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The increase of earthquakes is believed to be the result of disposing wastewater from hydraulic fracturing, or fracking, according to the report. Fracking involves high-pressure injections of toxic water into the Earth’s surface in order to extract oil and natural gasses.
While the process itself is not believed to be responsible for earthquakes, scientists believe that it may be a problem specific to Oklahoma and are exploring the root causes.