Apparent cause determined for Texas quakes

DALLAS, March 15 (UPI) -- U.S. scientists say they've determined the possible cause of a series of small 2008 and 2009 earthquakes near the Dallas-Fort Worth International Airport.

The Southern Methodist University and the University of Texas at Austin research showed operation of a saltwater injection disposal well in the area was a "plausible cause" for the series of small earthquakes that occurred between Oct. 30, 2008, and May 16, 2009.

The quakes occurred in an area of North Texas where the vast Barnett Shale geological formation traps natural gas deposits in subsurface rock. The research led by SMU seismologists Brian Stump and Chris Hayward determined the shale production relies on the injection of pressurized water into the ground to crack open the gas-bearing rock -- a process known as "hydraulic fracturing" -- with some of the injected water being recovered in the form of waste fluids that require disposal.

Although the scientists said the quakes do not appear directly connected to the drilling, hydraulic fracturing or gas production, the study concludes re-injection of waste fluids into the shale might have caused the earthquakes.

"It is plausible that the fluid injection in the southwest saltwater disposal well could have affected the in-situ tectonic stress regime on the fault, reactivating it and generating the DFW earthquakes," the scientists said.

The study appears in the journal The Leading Edge.