Huge quakes may foretell smaller, human-caused ones

Distant powerful temblors triggered ominous activity at wastewater injection sites

Over  the last few years, the number of earthquakes in the central and eastern United  States has increased along with the rise in wastewater disposal wells  associated with fracking. The map shows all of the magnitude 3 or greater  earthquakes that occurred in the United States in 2009-2012. Places with the  highest natural earthquake hazards are shown in red and orange while areas with  lower risk are shown in yellow and green.

Courtesy of Science/AAAS

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