Fracking may cause more earthquakes than initially thought, according to an article in this week’s Proceedings of the National Academy of Sciences.
At least 59 “small-magnitude” earthquakes of 1.4 to 2.5 magnitude occurred over a two-year period ending in September in the Barnett Shale region of Texas that were never reported by the National Earthquake Information Center, said Cliff Frohlich, a senior research scientist at the Institute for Geophysics at the University of Texas at Austin.
Many of those earthquakes happen when fluids are injected into the ground to release natural gas, a process called hydraulic fracturing that may also relieve the friction between tectonic plates, said Frohlich, who wrote the article. The U.S. Geological Survey typically collects data for seismic events at least 3.0 in magnitude.
“Rather than just looking at earthquakes when a crash happens, let’s go look for ones that may not be bothering people and see if there are trends,” Frohlich said in a telephone interview.
These “triggered” events may be exacerbated by fracking along fault lines, and differ from “induced” events that happen solely because of human actions, such as a man-made lake weighing down and compressing a land mass, Frohlich said.
He used seismological data from EarthScope USArray, 400 connected seismographs spaced 70 kilometers (44 miles) apart. They’re relocated within the U.S. every two years and were in Texas from November 2009 through September 2011.
“I can’t study the whole country, but one field at a time I can go in and say, ‘This is what the data say,’” he said.
More research on triggered events is needed to better understand what causes them and how they may be avoided, Frohlich said.
“The data’s freely available,” he said. “A junior high school student could download the data and do what I did -- if they were familiar with seismology.”