The dots appear sporadically at first. Then they start bursting forth like popcorn.
An animated map posted by the US Geological Survey office in Oklahoma recently illustrates the dramatic growth in the number of earthquakes rattling the Sooner State in recent years, a surge scientists have linked to the underground injection of wastewater from oil wells.
Oklahoma became the nation’s seismic hot spot a few years ago, as hundreds of small-to-moderate earthquakes began shaking the state. Before 2010, it typically had two or three tremors a year of magnitude 3.0 or bigger; the number soared to 903 in 2015. By mid-2016, the USGS warned that 7 million people living between northern Texas and south-central Kansas were at risk of a damaging earthquake, leaving scientists and government officials scrambling to get a handle on the problem.
Though popularly tied to hydraulic fracturing, which uses high-pressure water to bore oil and gas wells into shale rock, the quakes aren’t the result of the “fracking” process itself. Once they’re drilled, wells in the area draw up 10 gallons or more of the salty wastewater with every gallon of oil. And the oil and gas boom that fracking produced led to a huge increase in the amount of wastewater that needed to be eliminated.
That water is usually disposed of with wells that can reach more than a mile below the surface. Scientists say that brine has lubricated long-dormant faults, causing them to slip and cause earthquakes.