While past studies have linked fracking to earthquakes, scientists now say the drilling method is also a source of even small seismic tremors.
With hydraulic fracturing, or fracking, drillers inject fluids underground to crack open hard rock and access oil and natural gas underneath. This process, and the underground disposal of the resulting wastewater, can add pressure to fault lines, triggering earthquakes. Past research linked the 2000s fracking boom to a record number of quakes in Texas, Kansas, and Oklahoma, but scientists could not determine if fracking also caused gentler rumbles. Looking at data from seismometers, it was difficult to tease out small, fracking-induced tremors from other vibrations.
“Seismometers are not smart. You could drive a truck nearby, or kick one with your foot, and it would record that vibration,” study coauthor Abhijit Ghosh, a geophysicist at University of California, Riverside, said in a statement. “That’s why for some time we didn’t know for sure if the signals were related to the fluid injections.”
The new research overcomes this hurdle. For the study, scientists installed seismometers around a Kansas fracking site and measured vibrations for more than eight months. Comparing the measurements with the site’s injection schedule, and adjusting for background vibrations, they found that small tremors near the injection site only emerged during fracking.
“We did not detect the tremors before or after the injections, which suggests the tremors are related to them,” Ghosh said. The findings, published in Science, could help researchers better gauge how fracking stresses underground rock.