A team led by Stanford University geophysics professor William Ellsworth has linked a 2012, 4.8 magnitude East Texas earthquake to human activity in an article published in the Science journal Thursday. Specifically, Ellsworth and his team found, wastewater injection stemming from hydraulic fracturing at a nearby well likely caused the tremor in the Texas town of Timpson.
“Our research is the first to provide an answer to the questions of why some wastewater injection causes earthquakes, where it starts and why it stops,” Ellsworth said in announcing the findings.
Ellsworth and his fellow researchers used a radar-based remote sensing technique called interferometric synthetic aperture radar (InSAR) to measure ground deformations near the wells that surrounded the sight of the Timpson quake. The radar waves can measure subtle changes in the ground, in this case from satellites.
During the study, according to Ellsworth, InSAR detected surface uplift in areas of Texas as far as five miles from disposal wells. Combined with increases in underground pressure that can result from wastewater disposal, surface uplift can cause earthquake activity.
The study found differences in the effects of deep and shallow injection sites. At the shallow wells, the pressure migrated upwards and subtly deformed the land above by several centimeters. At the deep-well injection sites in east Texas, the combination of stiffer rock and the impermeable formation above allowed the rising pressure to build up below until it triggered the 2012 earthquakes along an ancient fault line.
A news release issued by Stanford notes that "the quakes ended in late 2013, when pressures began to decline after wastewater injections were scaled back considerably."
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Ellsworth's study is the strongest link yet between fracking activity and Texas earthquakes. A previous study conducted by UT-Austin researchers into the Timpson quake only said that it was "plausible" that the tremor was caused by fracking. The UT team based its conclusion on a sophisticated computer model and likely disposal methods to build a theory of the quake, rather than any concrete evidence.
Figuring out how to prevent uplift and lower underground pressure is the key to reducing the likelihood of earthquakes in regions that are currently being fracked, Ellsworth said.
“Moving forward, we need to predict where pressures will increase in order to reduce the potential for inducing earthquakes,” Ellsworth said. “Our research uncovers new possibilities for operating wells in ways that reduce earthquake hazard.”
The Texas Railroad Commission, which is charged with monitoring the safety of disposal wells in Texas, did not immediately respond to a request for comment. In previous cases, it has found scientific evidence linking seismic activity to fracking to be inconclusive, most recently when it refused to find disposal wells in operation near the Azle and Reno earthquake cluster in 2014 to be responsible for the quakes.