Using satellite imagery, the researchers found that a series of earthquakes that struck Texas between 2012 and 2013- including the largest-ever quake recorded in eastern Texas-were caused by the injection of large volumes of wastewater from oil and gas activities into deep underground wells. But now, in a study published Thursday in Science, researchers have fastened another nail in the “man-made earthquakes” coffin.
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As increasing pore pressure within a geologic fault is known to be able to cause the two sides of the fault to slip and release seismic energy as an natural disaster, the combination of stiffer rock and the impermeable “blocking formation” above at the deep-well injection sites allowed the rising pore pressure to migrate downward and build up until it triggered earthquakes in 2012 along an ancient fault line.
“Monitoring surface deformation using these remote sensing techniques is a proactive approach to managing the hazards associated with fluid injection, and can help in quake forecasting”, explained Manoochehr Shirzaei, a geophysicist and assistant professor at ASU’s School of Earth and Space Exploration and lead author of the study, in a press release.
Ellsworth explained that when wastewater injections were significantly decreased, shaking in the ground also stopped. The terrain between two of the wells lifted about 3 millimeters a year on average from May 2007 through November 2010. With the help of radar satellites, scientists have obtained data that has identified five man-made earthquakes in the southern US state. Every day, two billion gallons of this wastewater is injected into roughly 180,000 disposal wells scattered throughout states such as Texas, California, Oklahoma and Kansas. The eastern wells were shallow and the satellite radar showed that the eastern wells weren’t the culprit, but the high-volume deeper western ones were, Ellsworth said. This explains why wastewater injections can, but not always, producing earthquakes. The ever-expanding pore pressure then reached fault zones, thus triggering earthquakes.
This did not happen at the shallow well sites in East Texas because a thick layer of almost impermeable rock beneath the injection sites of the shallow wells prevented the pore pressure from migrating downward towards the crystalline basement, a deep and faulted rock layer where earthquakes originate. A new study has revealed that wastewater injections into the Earth at oil and gas plants can lead to earthquakes.
The team says that these man-made earthquakes have stopped.
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But where that wastewater is injected can make a huge difference. Shirzaei indicated he was neither pro or against fracking. “The recent upturn in seismicity in Oklahoma and Kansas commonly happens where injection occurs close to the crystalline basement, so we’re getting lots of earthquakes in those places”, Ellsworth said.
