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The study, published Tuesday in Seismological Research Letters, reports that fracking waste injection wells are now the leading cause of earthquakes in Texas. Hydraulic fracturing, or fracking, involves thrusting chemicals and water against shale rock to break it up and release oil or gas. The process produces large amounts of waste fluid, or brine, that is either recycled or disposed of in injection wells.
Fracking itself can also induce earthquakes, but the technique has never caused earthquakes greater than magnitude 4. For comparison, an Oklahoma injection well is thought to have triggered a magnitude-5.6 earthquake in 2011. Mining blasts and geothermal energy plants can also trigger earthquakes. Quake road map.