After one of the strongest earthquakes ever to hit Oklahoma struck Saturday, state regulators ordered oil and gas companies to shut down all their wastewater disposal wells in a 725-square-mile area around the site of the quake's epicenter near Pawnee.

The seismic activity immediately raised suspicions that it was linked to injection wells that oil and gas companies use as part of fracking and other operations. The 5.6-magnitude earthquake was felt in five states; it followed a string of smaller temblors that hit the region in Oklahoma in the past week.

As Joe Wertz of StateImpact Oklahoma reports for our Newscast unit:

"The U.S. Geological Survey says the quake resembles ones scientists have linked to the wells, which the energy industry fills with fluid from oil and gas production — a small amount of which is from fracking."Dave Denny lives near the epicenter. The quake damaged the foundation of his trailer home and severed his sewer line." 'It's a bad thing to wake up to, let me put it that way,' Denny says. 'Luckily, everybody is alright and all this can be repaired.'""Researchers say disposal wells are likely the reason Oklahoma is now the most seismically active state in the country."

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