The number of significant earthquakes in the Midwest has increased almost fivefold in the last four years. Researchers with the United States Geological Survey set out to discover why.

Though fracking causes tiny tremors, USGS scientists were unable to link those interruptions in the earth’s crust directly to large, recurring temblors. But they did notice the new quakes typically occurred around wells used to dispose of tremendous amounts of wastewater produced by fracking — cavities that go deeper than gas drilling wells to levels where faults and stresses are more common. And flooding those levels with high-pressure fluid can make earthquakes more likely. –ARK

Alyssa Battistoni at Mother Jones:

[T]he recent surge of fracking activity, which uses millions of gallons of water to crack rock deep in the ground and release natural gas, has boosted the volume of wastewater being injected into the ground.

… Many wastewater wells actually go deeper than gas drilling wells, reaching an older layer of rock known as basement rock, where stresses and faults are more common. The high pressure used to pump water into waste wells can cause those faults to shift, and the water itself can lubricate already-stressed faults, easing their movement and making an earthquake-causing slip more likely. As [USGS seismologist Bill] Ellsworth told NPR, “Small perturbations can tip the scales, allowing an earthquake that might not otherwise happen for a very long time.”

… We don’t yet know why only a few of the tens of thousands of wastewater disposal wells have induced earthquakes, or whether any specific planned well is particularly likely to cause a quake. It could be because production has ramped up and the sheer quantity of wastewater has increased, or because oil and gas companies are using new techniques for injecting waste fluids. And while there have been no confirmed cases of major earthquakes resulting from the injection of wastewater into the ground near major faults, the possibility can’t be eliminated, says Deputy Secretary of the Interior David Hayes.

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