A new study has found that fluid injections deep underground are causing more earthquakes than previously believed. Fluid injections have been becoming more prevalent with the recent increase in the practice of hydraulic fracturing, also known as fracking. Fracking is a drilling technique that pumps millions of gallons of water mixed with chemicals and sand under high pressure into the ground to break up rock and release natural gas.
Researchers already knew that fluid-injection operations can cause earthquakes and have already linked fracking to Oklahoma’s strongest recorded earthquake in 2011. There has also been over 180 tremors in Texas between October 30, 2008 and May 31, 2009 that are believed to be caused by fracking operations.
To learn more about how fracking is causing these earthquakes Cliff Frohlich, a seismologist from the University of Texas at Austin, analyzed seismic activity in the Barnett Shale of northern Texas between November 2009 and September 2011. By placing mobile seismometers over approximately 23,000 square-miles he found the epicenters for 67 earthquakes with magnitudes of 3.0 or less on the Richter scale. This was more than eight times over what was reported by the National Earthquake Information Center. The majority of the earthquakes occurred within a few miles of one or more injection wells, which suggests that the injection-triggered quakes are more widespread than thought.
Frohlich discovered that a third of the earthquakes detected were grouped together into eight geographic regions. He found that all of the wells nearest to these areas had high rates of fluid injection, which exceeded 150,000 barrels of water each month. This has led him to believe that fluid injection may trigger earthquakes by reaching and relieving friction on a nearby fault. Frohlich posted his findings online on August 6 in the journal Proceedings of the National Academy of Sciences. He is looking to further his investigations by studying fracking operations in other areas, such as the Marcellus Shale on the East Coast, to see if there is a cutoff in terms of what volume of fluid injection might cause earthquakes.