New Republic : “Oklahoma had more earthquakes with over 3.0 magnitude this year than California—241 to 140, as of June. And in just 14 hours last weekend, Oklahoma registered three of a total seven quakes over that magnitude.”  

‘The question is whether these Oklahoma quakes are natural. Scientists
increasingly believe that fracking by the oil and gas industry is triggering earthquakes in regions that otherwise should be relatively stable. Fracking itself isn’t to blame, they say, but the large amount of wastewater produced in the process.”  

“That’s not to say fracking wastewater always leads to earthquakes … Very few of the 35,000 wastewater injection sites nationwide end up causing earthquakes, and even fewer quakes can be felt. And yet, a handful of wells can be linked to entire regions of seismic activity. For example, a recent study from Cornell University researchers in Science magazine found that four ‘modern, very high-rate injection wells’ were linked to earthquake activity near one Oklahoma town.”  

“Here, a graph from USGS shows how the rate of earthquakes over 3.0 has increased in central and eastern U.S., particularly since 2010:”