Sunday, January 5, 2014

FRACKING; USGS to make separate risk map for man-made quakes

Mike Soraghan, E&E reporter

Federal officials are wrestling with how to account for the hazard created by man-made earthquakes, many of which are triggered by oil and gas activities.

In the past, the U.S. Geological Survey has generally excluded shaking related to industrial activity from its earthquake hazard maps. The maps project the likelihood of large, natural earthquakes and are used to develop building codes, plan roads and bridges, and set insurance rates.

But amid an increase in the number and severity of man-made quakes in oil and gas regions, scientists and engineers at the agency are developing a separate map that will include what geologists call "induced seismicity."

The traditional hazard maps, predicting the risk of natural quakes, are expected to be issued early next year. The map evaluating the risks of man-made quakes will be issued later in the year because the agency is still figuring out how it should be assembled.

Locations of earthquakes linked by scientists to human activity as of last year. Click the map for a larger version. Map courtesy of the National Research Council.

"It's been the subject of rather intense discussion," said Bill Leith, senior science adviser for earthquake and geologic hazards at USGS headquarters in Reston, Va.

The traditional map of natural earthquakes is intended to guide decisions by architects, builders and others for as long as 50 years. The danger from man-made quakes might be much shorter than that, particularly if the activity causing it stops.

Still, man-made earthquakes are a hazard. Two people were injured and 14 homes were destroyed in a November 2011 quake outside Oklahoma City that USGS researchers have linked to deep underground injection of oil and gas wastewater (EnergyWire, March 27).

The amount of such deep injection has grown sharply with the nation's shale drilling boom, which has been driven by a hydraulic fracturing process that uses far more water than conventional drilling and creates far more wastewater. Most of that wastewater is eventually injected underground.

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