About 99 percent of the earthquakes occurring in Oklahoma the past few years are located within nine miles of a certain type of injection well, a state agency reported Tuesday.
During recent days, weeks and months, parts of Edmond and Logan County have been shaken by earthquakes strong enough to damage the Logan County jail and several homes. Quakes have been felt in the Arcadia Lake and Jones area.
Tuesday, the Oklahoma Geological Survey released a position statement dated Feb. 17.
It begins noting the significant increase in seismic activity in the state since 2009. Most of the quakes are not strong enough to be felt, but those that are draw interest from citizens.
“This statement communicates what, in the opinion of the OGS, the data currently tells us and outlines our plans for monitoring future activity and conducting research to better understand Oklahoma seismicity,” the authors wrote.
Since 2009, earthquake activity in Oklahoma has been about 40 times higher than in the previous 30 years, the authors stated. While more than 90 percent of these earthquakes are too small to be felt, they are recorded by the OGS network.
Based on reported “felt” quakes before creation of the OGS network, this recent level of activity is significantly greater than the past 100 years. Even a 100-year time frame is not statistically representative in geological terms, the authors stated.
Most of the historical and more recent earthquakes are located on or near the Nemaha Ridge, the Ouachita-Arbuckle-Wichita Mountain front and other major geological structures, the authors stated.
Implied fault movements for the majority of the earthquakes appear to be consistent with natural stresses in Oklahoma, the authors stated.
Regarding the possible relationship between recent earthquakes and oil and gas activities, the authors made the following observations:
• It has long been recognized by scientists that both fluid injection and withdrawal in the subsurface can trigger earthquakes by altering conditions on naturally occurring faults near failure;
• Fluid injection associated with oil and gas activity including enhanced oil recovery, hydraulic fracturing and waste water disposal has occurred for a long time in Oklahoma. More than 100,000 wells have been hydraulically fractured here since 1948;
• About 4,000 active saltwater disposal wells exist in the state (about 30,000 nationally). Recognized occurrence of triggered seismicity related to these wells are rare;
• About 80 percent of the state is within 9 miles of an Underground Injection Control Class II water disposal or enhanced oil recovery injection well. For this reason, identifying possible induced or triggered seismicity requires more scientific evidence than simply identifying spatial correlations. During recent years, about 99 percent of the earthquakes in the state have occurred within 9 miles of this type of well;
• A direct link of the Jones earthquake swarm to the oil and gas activity cannot be established at this time.
Research into the cause of the earthquakes will continue on several fronts, the authors stated. Future studies could include activity in the vicinity of Prague, Jones, Arcadia Lake, in Love County and other appropriate studies.
The Oklahoma Geological Survey is increasing its resources in the area of earthquake seismology, providing additional capability to not only improve the agency’s monitoring and reporting of earthquakes, its primary duty, but also to better understand key concepts within the context of Oklahoma seismicity and to communicate them to the public.
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