The 2013 earthquake swarm that centered around the town of Azle in Tarrant County was likely the result of natural gas drilling and wastewater injection, according to a report published Tuesday in the Nature Communications journal.
According to Matthew Hornbach, an SMU associate professor of geophysics and lead author of the study, high injection rates to the west of a previously dormant fault, combined with high removal rates on the east side of the fault, created a pressure differential that led to the tremors, which topped out in November and December of 2013 with two 3.6 magnitude quakes.
Certain ancient faults in the region, like the one in Azle, are already "nearly critically stressed" because of their orientation and direction, Heather DeShon, another SMU professor and study co-author said in a press release.
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"What we refer to as induced seismicity -- earthquakes caused by something other than strictly natural forces -- is often associated with subsurface pressure changes," DeShon said. "We can rule out stress changes induced by local water table changes. While some uncertainties remain, it is unlikely that natural increases to tectonic stresses led to these events."
The team behind the report says that in two of the other earthquake swarms that have occurred in North Texas -- the ones centered near DFW airport and Cleburne -- injection wells were found to be possible causes for the earthquakes. In the Azle study, the "introduction of fluid pressure modeling of both industry activity and water table fluctuations" allowed the scientist to determine that drilling activity was the "most likely" cause of the Azle tremors.
"This report points to the need for even more study in connection with earthquakes in North Texas," Brian Stump of SMU said. "Industry is an important source for key data, and the scope of the research needed to understand these earthquakes requires government support at multiple levels."
When asked for comment, Craig Pearson, the in-house seismologist for the Texas Railroad Commission -- the state agency that oversees oil and gas activity in the state -- told The Dallas Morning News that "the study raises many questions with regard to its methodology, the information used and conclusions it reaches."