U.S. to Map the Risks of Man-Made Earthquakes
ANCHORAGE, Alaska—A rise in the frequency of earthquakes in regions with increasing oil and gas extraction is prompting scientists for the first time to assess risks of man-made quakes and include them on federal maps that influence building codes and public policy.
The new mapping, which the U.S. Geological Survey hopes to release later this year, is likely to put regions of the central U.S. not typically thought of as earthquake zones on notice for greater seismic hazards. Unlike West Coast states at high risk for major quakes, like California, other areas typically aren't as prepared to handle strong temblors.
The USGS regularly maps hazards from naturally occurring quakes, alerting building engineers and local governments to the probability of moderate and strong shaking in their regions based on fault lines and seismic studies. The agency said that in the wake of research showing increased seismic activity in certain regions—including two strong 2011 quakes in Colorado and Oklahoma—it decided to release a separate map to evaluate the risk of man-made quakes, called induced quakes.
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An average rate of more than 100 earthquakes a year above a magnitude 3.0 occurred in the four years from 2010 to 2013 in the central and eastern U.S., compared with an average rate of 20 events a year observed from 1970 to 2000, according to the USGS... The mapping effort comes as regulators, industry officials, politicians and scientists begin to grapple with how to measure and respond to potential quake risks from human activities in the aftermath of a jump in seismic activity in Oklahoma, Texas, Arkansas, Ohio and Colorado.
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Wastewater disposal after oil extraction appears to cause larger quakes than fracking, researchers said. In that process, oil is extracted with salt water. The remaining brine, or wastewater, is injected into the ground. The pressure caused by that can put stress on an existing faults and trigger quakes, some scientists contend... On Thursday, new research unveiled at the Seismological Society of America conference said that quakes can be triggered up to 30 miles away from the site of wastewater disposal, a greater distance than previously thought, said Katie Keranen, an assistant geophysics professor at Cornell University who led the study.
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