In an article published late last month in the journal Nature Communications, researchers at Southern Methodist University pointed to hydraulic fracturing activities as the probable cause of an increase in earthquakes near Azle, Texas, based on a study they had conducted in the area. The researchers’ conclusion conflicts with the stance of the U.S. Geological Survey that the cause of the earthquakes is inconclusive.
In the study, the SMU researchers analyzed data from the U.S. Geological Survey’s National Earthquake Information Center, which reported that from early November 2013 through January 2014, there were 27 earthquakes near the cities of Azle and Reno, Texas. Since 2008, the northern region of Texas has experienced four swarms of earthquakes, with 130 total quakes. Most of the earthquakes have been relatively small, but citizens have expressed concern about the uptick, particularly since the U.S. Geological Survey reports that the area had only one recorded earthquake in the 58 years before 2008. In the article summarizing the findings of their study, the SMU researchers stated that “while some uncertainties remain, it is unlikely that natural increases to tectonic stresses led to these events.”
To facilitate the study, the SMU research team created temporary seismic stations in the Azle area in December 2013. The researchers conducted a first-of-its-kind modeling study to clarify the locations of the faults that are the sources of the earthquakes. The modeling analyzed the changing pressure in the rock formation from two wastewater injection wells and more than 70 production wells that produce natural gas and brine. The study suggests that the pattern and position of many of the earthquakes form a linear trend.
A major obstacle to fully identifying whether hydraulic fracturing-related activities have been causing the earthquakes in Texas is that much of the property where hydraulic fracturing occurs is privately owned. To facilitate a more in-depth investigation of the issue, the Texas Railroad Commission hired seismologist David Craig Pearson in March of last year to study “the impact of oil and gas extraction activities on the day-to-day lives of Texas residents” and to “examine any possible correlation between seismic events and oil and gas activity.” Commenting on the SMU study, Pearson said that he needs “more time to digest the study and meet with its authors.”
George Choy, a U.S. Geological Survey research geophysicist, also commented on the study. Choy said that “there just isn’t enough evidence to support the claim yet in this case. I don’t think that has been proven yet. There are some nearby wells that have been inactive for a while. The connection has not been established, but we cannot rule them out. … We cannot make a correlation with any wells without knowing their history.”
Industry group Energy In Depth Texas expressed similar concerns, but commended the SMU research team for building on past analyses with industry data and statewide subsurface knowledge. In a statement on its website, Energy In Depth Texas said that despite its concerns about the researchers’ conclusion, “this kind of active collaboration bodes well for all interested stakeholders – not just scientists and regulators, but also the general public, which wants to know what is being done to address their concerns about earthquakes.”
The article “Causal Factors for Seismicity Near Azle, Texas” was published online by the journal Nature. It is available here.