The U.S. Geological Survey (USGS) and Oklahoma Geological Survey jointly issued a rare earthquake warning this week for parts of central Oklahoma after a major increase in seismic activity there.
Concerned that the increased seismic activity may indicate a higher risk for a larger, damaging earthquake of 5.0-magnitude or greater, both agencies issued the advisory, the first-ever such warning issued for a state east of the Rockies.
Seismic hazard statements are more typically issued for western states such as Alaska and California. However, there have been almost as many tremors shaking Oklahoma as California this year, which led to the USGS’s and Oklahoma Geological Survey’s concerns.
Robert Williams, a research geophysicist at the U.S. Geological Survey’s Earthquake Hazards Program in Golden, Colorado, told LiveScience “We haven’t seen this before in Oklahoma, so we had some concerns about putting a specific number on the chances of it. But we know from other cases around the world that if you have an increasing number of small earthquakes, the chances of a larger one will go up.”
The number of earthquakes in Oklahoma has outpaced the number of quakes in California for the first few months in 2014, and there have been 2,500+ tremors in Oklahoma since 2012 (Watch 2500+ Oklah oma Earthquakes Since 2012 Video). In addition, the USGS reports that “the number of quakes magnitude 3 and stronger jumped by 50 percent in the past eight months in Oklahoma. Some 183 earthquakes of magnitude 3 or greater struck between October 2013 and April 2014. The state’s long-term average from 1978 to 2008 was only two earthquakes of magnitude 3.0 or larger per year.”
In November 2011, a 5.6-magnitude quake centered near Prague, Oklahoma, destroyed 14 homes and injured at least two people. That quake was linked directly to the injection of wastewater from oil extraction into the ground. According to a study published in the journal “Geology,” the 5.6-magnitude central Oklahoma quake was “…the largest wastewater-induced earthquake ever recorded.”
Wastewater injection has been linked to earthquake activity since the 1960s, when it caused a series of earthquakes around the Denver, Colorado, area. In the process of oil extraction, wastewater is typically forced up as well. Oil companies often pump the wastewater back into the wells where it then fills the porous spaces in the rocks and acts as a lubricant, which can cause slippage and seismic activity.
Scientists originally believed that the earthquakes produced by wastewater injection would be fairly benign, mostly in the magnitude 3-to-4 range. However, after the November 2011 5.6-quake in central Oklahoma, they now realize these types of man-made earthquakes can get much larger. But just how much larger is yet to be known.
Katie Keranen, a geophysicist at Cornell University and former seismologist at Oklahoma University, says “We don’t know what the maximum size of earthquakes could be that we could trigger from disposal.”
Keranen released a paper recently which showed how four high-volume wastewater injection wells in Oklahoma triggered a rash of small earthquakes over 9 miles away.
“Our results, using seismology and hydrogeology, show a strong link between a small number of wells and earthquakes migrating up to 50 kilometers (31 miles) away,” said Keranen in a press release. Reason enough, one would think, not to continue this practice!
Although the process which caused the 5.6-magnitude quake in central Oklahoma wasn’t directly related to hydraulic fracturing, aka “fracking,” fracking also involves injecting water, sand and other substances into the ground under high pressure, carrying similar risks. There have been a number of recent incidences involving fracking and earthquakes as well.
In 2011, a 5.8-magnitude quake on the East Coast, centered near Mineral, Virginia, was felt in more than a dozen states and several Canadian provinces. The area where the quake was centered is rich in natural gas and is heavily covered with drilling sites which use fracking to retrieve the gas. The area had limited seismic activity before the introduction of fracking.
West Virginia (like Virginia and Oklahoma) was a state with minimal seismic activity until fracking began in 2009, when it began to see an uptick in seismic activity with numerous 2.2-to-3.4-magnitude tremors reported. Oil and gas officials were quick to dismiss a correlation between fracking and increased seismic activity, however, the “coincidence” of the startup of fracking and earthquakes in a seismically quiet area is notable.
Similar occurrences have been reported elsewhere. In Arkansas, earthquakes began occurring when fracking practices were initiated. Near Basil, Switzerland, a 3.4-magnitude earthquake occurred after a 3-mile deep well was drilled into a geologically quiet area. The Swiss were quick to make the connection and immediately shut the well down.
It will probably be a different story in Oklahoma, however, as oil made Oklahoma.
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