Forget California—Oklahoma is now the most earthquake prone state in the lower 48, according to the U.S. Geological Survey. And in this case, the reason appears to be man-made.

More than 900 magnitude 3.0+ earthquakes shook the state last year. So far in 2016, two earthquakes exceeded 5.0 – causing damage in several areas.



Scientists are pointing the finger at the oil and gas industry. Hydraulic fracturing, also referred to as fracking, is a method to extract oil and gas from the earth, and it's been around for decades. However, the amount of fracking dramatically increased in the last few years, helping drive U.S. oil domestic production to near 9 million barrels per day.



According to the Energy Information Administration (EIA), the number of fracking wells in the U.S. went from 23,000 in 2000 to 300,000 wells in 2015. Meanwhile, the output of oil from these wells made up more than 50 percent of the U.S. daily oil production last year.



But it's not necessarily the fracking that's causing Oklahoma's earthquakes: It's the disposal of fracking wastewater.