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.

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. www.washingtonpost.com/...