Mother Nature may have given California earthquakes, but could the oil and gas industry be giving the same treatment to parts of Oklahoma, Kansas, Texas, Colorado, New Mexico and Arkansas? According to a study that the U.S. Geological Survey published Monday, about 7 million Americans now live in areas almost as prone to earthquakes as the Golden State, thanks in part to wastewater disposal from drilling oil.

“By including human-induced events, our assessment of earthquake hazards has significantly increased in parts of the U.S.,” said Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project, in a statement. “This research also shows that much more of the nation faces a significant chance of having damaging earthquakes over the next year, whether natural or human-induced.”

Induced earthquakes often occur due to large amounts of chemical-laden fluids being injected into underground wells. The process loosens faults and makes them more likely to slip. Hydraulic fracturing, better known as fracking, is sometimes the cause itself as well, though rarely, according to the report. The process includes blasting millions of gallons of chemical-filled water underground to break apart shale deposits and release gas. That water then is also put into underground wells.

Already, USGS has recorded more than a tenfold increase of earthquakes in the last six years in the central U.S., with an average of 318 per year of magnitude 3.0 or stronger. From 1973 to 2008, there were an average of 24 earthquakes of magnitude 3.0 reported yearly. In 2015, there were 1,010 earthquakes reported, the report said.

While most earthquakes are minor, some major ones have been reported. In 2011, Oklahoma experienced a powerful, magnitude 5.6 earthquake that many linked to wastewater injection, the Washington Post reported. On a USGS map, an area of Oklahoma was featured with more red – indicating the geographical chance of earthquake activity – than California.

"People living in areas of higher earthquake hazard should learn how to be prepared for earthquakes," the USGS report advised.