Spike in tremors linked with injection of wastewater from fracking
By Summit Voice
FRISCO — Federal and state geologists say there’s an increased risk of a strong earthquake in Oklahoma after the overall rate of quakes increased by about 50 percent since late 2013.
After statistically analyzing the increased rate of earthquakes, the scientists said they’re fairly certain it’s not just natural variability — deep injection of waste water from fossil fuel exploitation is seen as a likely cause.
“We hope that this new advisory of increased hazard will become a crucial consideration in earthquake preparedness for residents, schools and businesses in the central Oklahoma area,” said Dr. Bill Leith, USGS Senior Science Advisor for Earthquakes and Geologic Hazards. “Building owners and government officials should have a special concern for older, unreinforced brick structures, which are vulnerable to serious damage during sufficient shaking.”
Between October 2013 and April 2014, there were 183 quakes of magnitude 3.0 or stronger. The long-term average between 1978 and 2008 was about two such quakes every year. The increased frquencny of small and moderate shocks ups the likelihood of future, damaging earthquakes in central and north-central Oklahoma.
Deep injection of wastewater into deep geological formations can increase pressure underground and even lubricate faults, in a well-known process called injection-induced seismicity. Much of this wastewater is a byproduct of oil and gas production and is routinely disposed of by injection into wells specifically designed and approved for this purpose.
Oklahoma’s heightened earthquake activity since 2009 includes 20 magnitude 4.0 to 4.8 quakes, plus one of the two largest recorded earthquakes in Oklahoma’s history – a magnitude 5.6 earthquake that occurred near Prague on Nov. 5, 2011, which damaged a number of homes and the historic Benedictine Hall at St. Gregory’s University in Shawnee.
As a result of the increased seismicity, the Oklahoma Geological Survey has increased the number of monitoring stations and now operates a seismograph network of 15 permanent stations and 17 temporary stations. Both agencies are actively involved in research to determine the cause of the increased earthquake rate and to quantify the increased hazard in central Oklahoma.