7 million Americans at risk of man-made earthquakes, USGS says

By:  Joel Achenbach

Earthquakes are a natural hazard — except when they're man-made. The oil and gas industry has aggressively adopted the technique known as hydraulic fracturing, or fracking, to shatter subsurface shale rock and liberate the oil and gas lurking there. But the process results in tremendous amounts of chemical-laden wastewater. Horizontal drilling for oil can also produce  massive amount of natural, unwanted salt water. The industry disposes of this wastewater by pumping it into deep wells.

And the Earth moves.

On Monday, the U.S. Geological Survey published for the first time an earthquake hazard map covering both natural and "induced" quakes. The map and an accompanying report indicate that parts of the central United States now face a ground-shaking hazard equal to the famously unstable terrain of California.

Some 7 million people live in places vulnerable to these induced tremors, the USGS concluded. The list of places at highest risk of man-made earthquakes includes Oklahoma, Kansas, Texas, Arkansas, Colorado, New Mexico, Ohio and Alabama. Most of these earthquakes are relatively small, in the range of magnitude 3, but some have been more powerful, including a magnitude 5.6 earthquake in 2011 in Oklahoma that was linked to wastewater injection.

Scientists said Monday they do not know if there is an upper limit on the magnitude of induced earthquakes; this is an area of active research. Oklahoma has had prehistoric earthquakes as powerful as magnitude 7.

It's not immediately clear whether this new research will change industry practices, or even whether it will surprise anyone in the areas of newly estimated risk. In Oklahoma, for example, the natural rate of earthquakes is only one or two a year, but there have been hundreds since fracking and horizontal drilling, with the associated wastewater injection, became commonplace in the last decade.

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