Energy companies deny a direct link between the earthquakes and the wells, citing a lack of evidence. The vast majority of the 35,000 disposal wells throughout Texas have reported no seismic activity, said Bill Stevens of the Texas Alliance of Energy Producers. Still, the alliance has created a task force to look into the phenomenon. "We feel comfortable that there is not a crisis," he said. "But we're also dedicated to pursuing it to the end."

The angst in North Texas has a familiar ring to it. Earthquakes in Colorado, Oklahoma, Ohio and Arkansas the past few years have all been tied to wastewater injection wells. New research presented at the Seismological Society of America annual meeting last month showed that disposal wells may be changing stress on existing faults and inducing earthquakes. While Reno and Azle residents have only reported around 30 earthquakes to the U.S. Geological Survey, area seismologists have recorded more than 300 quakes in the area since December – many too small for human detection – all clustered around area injection wells.

The earthquakes have been relatively small, less than a magnitude 4.0 – not big enough to cause major damage but alarming enough to spur state leaders into action. In March, the Texas Railroad Commission, which oversees the oil and gas industry, took the rare step of hiring a seismologist to study the matter. Earthquakes in Texas are historically rare. But in 2008, a rash of earthquakes began in the Dallas-Fort Worth area near where energy companies were fracking for natural gas, said Cliff Frohlich, associate director of the Institute for Geophysics at the University of Texas, who studied the tremors. Frohlich and others measured more than 60 quakes over a two-year period, all near injection wells.

Reno and Azle, as well as Dallas, sit on small fault lines several miles underground, Frohlich said. Wastewater blasted into disposal wells at high speeds could potentially disturb those otherwise dormant faults, causing them to slip and induce earthquakes, he said. However, faults also exist in South Texas, an area currently experiencing a fracking boom with thousands of wastewater wells, yet is reporting little to no seismic activity, Frohlich said. Also, the Bakken Shale in North Dakota is in the midst of an oil boom thanks to hydraulic fracturing – yet no earthquakes. "You can never prove 100% that earthquakes are caused by humans," Frohlich said. "But it's pretty suspicious."