Verge: Hydraulic fracturing, or fracking, is a technique in which natural gas is extracted from shale rock deep underground by injecting sand, water, and various chemicals into the rock to force the gas out. One side effect of fracking is microearthquakes, and a small percentage of them are strong enough to be felt by humans. Now, Robert Skoumal of Miami University in Ohio and his colleagues have shown that fracking was the direct cause of a period of earthquakes, including one of magnitude 3, centered near Poland Township, Ohio. Hydraulic fracturing began in the area in 2014, and during March of that year, 77 earthquakes were detected in a region that had previously never experienced any such seismic activity. When the fracking ceased, so did the earthquakes. Skoumal's team was even able to narrow down the source of the earthquakes to just a small portion of the field of wells. The researchers believe that the fracking activated a preexisting fault in the area, but they say there is no cause for alarm because fracking has not been shown to cause significant earthquakes.
