Scientists: Drilling, wastewater injection caused Azle earthquakes

It turns out natural gas drilling and wastewater injection are to blame for more than two dozen earthquakes in the Azle area, west of Fort Worth.

Seismologists at Southern Methodist University and the United States Geological Survey monitored the shaking.

"Our conclusion is that the most probable cause of the seismicity in the region has to do with oil and gas operations in the Azle-Reno area over the last few years," said Dr. Matthew Hornbach, SMU associate professor of geophysics.


They said removing saltwater from the wells in the gas production process and then injecting the wastewater back underground into a separate well is likely the cause of the quakes.

"We found the pressure associated with oil and gas injection of brine and removal of fluids create the largest pressure changes in the sub-surface where we see these earthquakes," said Hornbach.

The quakes are not directly caused by the controversial method of natural gas extraction known as fracking. However, the removal of wastewater is used in the fracking process.

The scientists said it's extremely likely that human activity, not random acts from Mother Nature, is causing the large number of quakes.

The study directly contradicts numerous statements from the Texas Railroad Commission that gas and oil activity isn't responsible for quakes around the state.


Before the quakes, the Azle-area had no recorded earthquakes for 150 years on faults that have been inactive for hundreds of millions of years.

When the volume of injections decreased, so did the shaking.

"This report points to the need for even more study in connection with earthquakes in North Texas," said Brian Stump, SMU's Albritton Chair in Earth Sciences. SMU scientists are also studying the outbreak of quakes that have been felt in the Irving and Dallas-area.

The results of the study didn't surprise Reno Mayor Lynda Stokes, who said the quakes caused damage even at city hall.

"I've been saying it all along, the citizens have been saying it," Stokes said. "It's kind of nice to hear SMU come back with this."

Irving is another hot spot for earthquakes despite having no active drilling sites, which baffles state experts.

Fifty-eight quakes have shaken North Texas since last April.

Unlike Azle and Reno, Irving only had two wells that were fracked. The state seismologist says because they didn't produce much, they were capped in 2010.

In February, SMU scientists discovered a fault line running from Irving into northwest Dallas from Hwy. 114 to Walnut Hill Lane.

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