Posted on June 23, 2014 by Mark Walker
On May 2, 2014, the U.S. Geological Survey and the Oklahoma Geological Survey issued a Joint Statement advising residents that the rate of earthquakes in Oklahoma had increased by 50% in the last seven months – “significantly increasing the chance for a damaging magnitude 5.5 or greater quake in central Oklahoma.” This is the first such advisory for a state east of the Rockies.
The Joint Statement was accompanied by the following graph which illustrates the dramatic rise in Oklahoma earthquake activity:
What accounts for this increase? The USGS’s statistical analysis indicated that the increase did “not seem to be due to typical random fluctuations in natural seismicity rates.” Instead, the “analysis suggests that a likely contributing factor to the increase in earthquakes is triggering by waste water injected into deep geologic formations.”
In November, 2013, the Groundwater Protection Council issued a White Paper summarizing its special session on “Assessing & Managing Risk of Induced Seismicity by Underground Injection.” The paper notes that there are approximately 150,000 UIC Class II permitted injection wells in the U.S., about half of which are disposal wells that inject into non-producing formations. Yet the number or felt earthquakes suspected to be associated with waste water disposal is very small (the White Paper focused on 8 examples), meaning induced seismicity from waste water disposal is “quite rare.” The concern seems to be focused around deep well injection into non-sedimentary basement rock or disposal in close proximity to critically stressed faults.
Earlier this year 14 Arkansas families filed lawsuits against two energy companies alleging that waste water disposal caused earthquake “swarms” in Arkansas in 2010 and 2011 which injured the plaintiffs’ property. Those swarms resulted in the plugging of several disposal wells and the imposition of a regulatory moratorium on new Class II disposal wells near the Guy-Greenbrier Fault.
The Oklahoma Geological Survey has developed a draft set of best practices for siting injection wells which seek to avoid placement of injection wells near known faults and injection into deep basement rock. The Oklahoma Corporation Commission is supporting research and the expansion of the network of Oklahoma seismic monitoring stations, and is following a stoplight approach to permitting new disposal wells which evaluates risk on a site-by-site basis.
P.S. While writing this I experienced two earthquakes (4.3 and 2.7 magnitude) at my home in Edmond, Oklahoma, within a one hour span. There have been seventeen earthquakes in Edmond within the past 8 days.