Oklahoma had 70 earthquakes in a week and they were probably caused by humans

As Oklahoma reels from more than 70 earthquakes over the last week, authorities are calling on energy companies to limit how much waste is injected into the ground.

The largest of the earthquakes hit a rural part of the state northwest of Oklahoma City on Wednesday night, and registered at 4.8 on the richter scale. Though no injuries were reported, it was felt throughout the state, according to the Weather Channel.

A report from the Oklahoma Geological Survey (OGS) last year found a connection between hydraulic fracturing (or fracking) and the increase in earthquakes the state has seen, especially “earthquake swarms,” or series of small earthquakes. That increase in earthquake activity has been sizable over the last few years. According to the state’s secretary of energy and environment there were 109 earthquakes in 2013 (based on earthquakes of magnitude 3.0 or greater, because that’s the level at which people can feel the tremors). In 2014, that number increased five-fold to 585 earthquakes. And though the records for 2015 aren’t available yet, “Estimates based on current earthquake activity show that 2015 will likely outpace previous year levels,” according to the agency.

Fracking involves using high-pressure water drilling to access oil and gas reserves for fuel. The OGS report found that though the drilling itself is not directly connected to the earthquakes, it’s likely that the man-made wells created to dispose of drilling waste water are causing the earthquakes. USA Today writes:

A state report last year noted a connection between hydraulic fracturing and some earthquake “swarms,” and state officials say there’s a potential risk to the public due to the increase in quakes. Experts say the quakes are likely being caused by injection wells, which are particularly deep wells into which drilling byproducts and wastewater are injected, rather than wells drilled to extract oil or gas.

“The OGS considers it very likely that the majority of recent earthquakes, particularly those in central and north-central Oklahoma, are triggered by the injection of produced water in disposal wells,” the agency said.

The government report confirmed the findings of another study published in the journal Science by Cornell University researchers in 2014, who looked at the increase in earthquake activity in Oklahoma between 2009 and 2013. They concluded that the wells that were linked to earthquakes had higher rates of disposal–meaning they injected waste water into the ground faster than the wells that didn’t seem to cause earthquakes. That could be because they raise pressure in the reservoir faster than when the waste is injected slowly, Science Mag writes.

Meanwhile one company involved in fracking, Sandbridge Energy, Inc., has said they won’t abide by the government’s request to scale back their waste disposal wells in the state, the Wall Street Journal reports. “Any directive by the Oklahoma Corporation Commission to the industry should be based on solid science—a position that is independent of our financial condition,” Sandridge spokesperson David Kimmel told the newspaper. The commission has, in response, filed court proceedings to make the company shut down the wells, according to KOCO.

Experts are concerned that there could be a larger earthquake in store for Oklahoma if the patterns continue. “I do think there’s a really strong chance that Oklahoma will receive some strong shaking,” geophysicist Daniel McNamara from the National Earthquake Information Center told the New York Times.