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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.
Earthquakes are caused mostly by slippage within geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. The underground point of origin of the earthquake is called the focus. The point directly above the focus on the surface is called the epicenter.