Oil and gas drilling has made parts of the central United States as dangerous as the most earthquake-prone regions of California, according to the U.S. Geological Survey (USGS), exposing millions of people to the risk of human-induced earthquakes, known as “frackquakes.”

According to new maps released on Monday by the USGS, roughly 7 million people who live and work in parts of Oklahoma, Kansas, Texas, Colorado, New Mexico, and Arkansas face “potential for damaging shaking from induced seismicity,” which the USGS notes is triggered primarily by wastewater disposal from oil and gas drilling activities.

“Within a few portions of the [Central and Eastern U.S.], the chance of damage from all types of earthquakes is similar to that of natural earthquakes in high-hazard areas of California,” the USGS states, with Oklahoma being the most prone to induced earthquakes and having the largest at-risk population.

Oklahoma has seen a rapid increase in earthquakes registering at or above a 3.0 magnitude per year, surging from 109 in 2013 to over 900 in 2015.

Last year, the state’s oil and gas industry regulator said that Oklahoma now experiences more earthquakes than anywhere else in the world, which scientists and officials have linked to the proliferation of disposal wells, which inject the toxic byproduct of oil and gas production deep underground.

“Today’s report once again highlights the dangers the fracking cycle poses to our communities,” declared Dan Chu, director of Sierra Club’s Our Wild America campaign, on Monday.

Connecting the rise of human-induced earthquakes to the other threats posed by the continued use of fossil fuels, Chu added, “The world is already experiencing deadly storms, droughts, and erratic climate and weather extremes due to climate change, and the rapid increase in earthquakes caused by wastewater injections from the oil and gas industry only raises the threat to communities across the country.”

The USGS’ one-year seismic hazard forecast for the Central and Eastern U.S. is the first predictive map to include human-induced earthquakes, in addition to natural earthquakes. Last spring, the government agency released another landmark map which highlighted the location and frequency of earthquakes thought to be caused by human activities.

Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project, said that “by including human-induced events, our assessment of earthquake hazards has significantly increased in parts of the U.S..”

Originally released on Common Dreams.