There's a reason State Farm wants to insure Johnson County homes against earthquakes. Injecting millions of barrels of fracking waste water loosens faults the way whiskey loosens tongues.

Cliff Frohlich of the Jackson School of Geosciences deployed seismographs throughout a 43-mile grid in the Barnett Shale. They detected eight times as many earthquakes as had been reported by National Earthquake Information Center, the clearinghouse for quake data. Each of the 24 reliably located epicenters was within two miles of one or more injection wells around Dallas/Fort Worth and Cleburne, handling 150,000 barrels of wastewater a day, according to the study published Monday in the Proceedings of the National Academy of Sciences.

Of course, not all injection sites were seismically active, he notes.

"It might be that an injection can only trigger an earthquake if injected fluids reach and relieve friction on a nearby fault that is already ready to slip," Frohlich says in a statement.

To nail that down, he'd have to look for evidence of faulting, or a lack thereof, near seismically active and inactive waste-water injection wells. This is the second such study to draw a link between injection wells and seismic activity. A report from the National Research Council reached the same conclusion in June.