Researchers said an analysis of seismic activity within two geologic regions in Texas supports the assertion that a series of earthquakes that has struck the area since 2009 were caused by human activity, with injected wastewater from oil and gas drilling in the Barnett Shale possibly to blame.
In a 13-page report published in the Nov. 24 issue of Science Advances, a magazine by the American Association for the Advancement of Science, researchers from Southern Methodist University (SMU) and the U.S. Geological Survey (USGS) analyzed fault displacements within the Fort Worth Basin (FWB) and the northern Mississippi Embayment (NME). The Barnett is within the FWB.
"To our knowledge, this is the first study to discriminate natural and induced seismicity using classical structural geology analysis techniques," wrote SMU's Maria Beatrice Magnani, Heather DeShon and Matthew Hornbach, who collaborated with the USGS's Michael Blanpied.
The researchers said their "most significant" discovery involved an analysis of fault displacements expressed in seismic reflection data. The data found no evidence of active faults for the past 300 million years in the FWB, but the NME has had active faults for the past 65 million years.
"Together, these results support the assertion that recent earthquake activity in the FWB is anthropogenic," the researchers said. They later added that based on their observations, "we must reject the hypothesis that these earthquake swarms are being triggered by tectonic forces.
“Rather, the data indicate that the FWB faults have experienced a remarkable lack of deformation in the past 300 million years, until the recent 2008 surge in seismicity, and independently confirm the interpretation by other authors of the recent seismic sequences in the FWB as induced rather than natural."
Another possible explanation is that the region is experiencing a long cycle of naturally occurring earthquakes, but the researchers cast doubt on that possibility.
"The alternative, unlikely case that the modern seismicity observed in the FWB is the effect of [an] exceptionally long rupture cycle of naturally active intraplate faults calls into question industry strategies that involve injections of large volumes of fluid at high rates near favorably oriented, critically stressed, active faults," they said.
According to the researchers, between 2008 and 2016, the rate of earthquakes in Texas measuring 3.0-magnitude or higher has increased from two to 12 per year. The increase has been highest in northeast and West Texas, regions with significant unconventional drilling and wastewater disposal through injection wells. In the FWB region in North Texas, the USGS's National Earthquake Information Center has cataloged more than 200 earthquakes, with at least 32 quakes measuring at least 3.0-magnitude and one temblor of at least 4.0.
Researchers analyzing seismic activity in neighboring Oklahoma have attributed earthquakes there to wastewater disposal via underground injection wells. Since 2015, regulators with the Oklahoma Corporation Commission have been attempting to mitigate the induced seismic activity by shutting down disposal wells within a 15,000-square mile area of the state.