Oil and gas development activities, including underground disposal of wastewater and hydraulic¹（液压的） fracturing, may induce earthquakes by changing the state of stress on existing faults to the point of failure. Earthquakes from wastewater disposal may be triggered at tens of kilometers from the wellbore, which is a greater range than previously² thought, according to research to be presented today at the annual meeting of the Seismological Society of America (SSA). As an indication of the growing significance of man-made earthquakes on seismic³ hazard, SSA annual meeting will feature a special session to discuss new research findings and approaches to incorporating induced seismicity into seismic hazard assessments⁴ and maps. The number of earthquakes within central and eastern United States has increased dramatically over the past few years, coinciding with increased hydraulic fracturing of horizontally drilled wells, and the injection of wastewater in deep disposal wells in many locations, including Colorado, Oklahoma, Texas, Arkansas and Ohio. According to the U.S. Geological Survey (USGS), an average rate of 100 earthquakes per year above a magnitude 3.0 occurred in the three years from 2010-2012, compared with an average rate of 21 events per year observed from 1967-2000.

 

"Induced seismicity complicates⁵ the seismic hazard equation," said Gail Atkinson, professor of earth sciences at Western University in Ontario Canada, whose research details how a new source of seismicity, such as an injection disposal well, can fundamentally alter the potential seismic hazard in an area.

 

For critical structures, such as dams, nuclear power plants and other major facilities, Atkinson suggests that the hazard from induced seismicity can overwhelm the hazard from pre-existing natural seismicity, increasing the risk to structures that were originally designed for regions of low to moderate seismic activity.

 

A new study of the Jones earthquake swarm⁶, occurring near Oklahoma City since 2008, demonstrates that a small cluster of high-volume injection wells triggered earthquakes tens of kilometers away. Both increasing pore pressure and the number of earthquakes were observed migrating away from the injection wells.

 

"The existing criteria⁷ for an induced earthquake do not allow earthquakes associated with the well activity to occur this far away from the wellbore," said Katie Keranen, assistant professor of geophysics at Cornell University, who led the study of the Jones earthquake swarm. "Our results, using seismology and hydrogeology, show a strong link between a small number of wells and earthquakes migrating up to 50 kilometers away" said Keranen. The study's result will be presented by co-author Geoff Abers, senior research scientist at Lamont-Doherty Earth Observatory⁸.

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