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When CSU graduate student Nicole McMahon was mulling over where, geographically, she would focus her thesis research in seismology, she chose to study earthquakes in Oklahoma. There were personal factors to her decision: She completed her undergraduate degree at the University of Oklahoma, her parents live in the Sooner State, and her sister enrolled this year at Oklahoma State University.
But she also knew that the state had recently become a hotbed of earthquake activity that would make for an interesting and important thesis.
In October 2015, a magnitude 4.5 quake struck not far from Cushing, Okla., but that was not as surprising as it might sound. Quakes of this size — and even larger ones — had been forecast by McMahon, CSU Professor Rick Aster, and scientists from the U.S. Geological Survey, Oklahoma State University, Saint Louis University, and Global Seismological Services.
According to the team’s research, published online earlier in October, “… very strong shaking levels … present the possibility of this potential earthquake causing moderate to heavy damage to national strategic infrastructure and local communities.” The statement was prescient and just a bit eerie.
Cushing is a major hub of the U.S. oil and gas pipeline transportation system and it is also one of the largest oil storage facilities in the world. An earthquake sequence that accelerated during October 2014 reactivated an intersection of structures within a fault zone, and the rest, as they say, is history.
Another earthquake, this one measuring 3.7 magnitude, took place Nov. 8.
“You’ve got faults in ancient rocks below the oil-producing formations that have been stressed, but inactive for many thousands, or even millions, of years,” said Aster, who heads the Department of Geosciences in CSU’s Warner College of Natural Resources.
“You then inject billions of gallons of wastewater from hydrocarbon production into deep earth formations.
While this can generally be a reasonable way to dispose of wastewater from energy production, in susceptible regions, this water spreads towards, or into, stressed faults, changing the hydrological and stress conditions. When you pressurize faults in this way it reduces the confining force that restrains them from slipping. That’s essentially why ancient faults are slipping and causing earthquakes in a number of regions across Oklahoma,” he said.
Aster is describing what creates an induced earthquake: a seismic event that would not have occurred without human influence, or at least not at today’s tremendously accelerated rates.
“THIS IS AN IMPORTANT TIME IN LOOKING AT AND UNDERSTANDING THE PROCESSES THAT THAT ARE DRIVING AN ACCELERATION OF HUMAN-CAUSED EARTHQUAKES IN OKLAHOMA. AT THE SAME TIME, WE ARE LEARNING ABOUT AND DEVELOPING NEW METHODS THAT WILL ADVANCE BASIC INDUCED AND NATURAL EARTHQUAKE SCIENCE IN A NUMBER OF IMPORTANT DIRECTIONS.”
It has long been known that induced earthquakes can be caused by filling reservoirs and by the injection or withdrawal of fluids into or from the earth. But Oklahoma has recently become the most remarkable induced earthquake laboratory on the planet.
“This is an important time in looking at and understanding the processes that are driving an acceleration of human-caused earthquakes in Oklahoma,” Aster said. “At the same time we are learning about and developing new methods that will advance basic induced and natural earthquake science in a number of important directions.”
Aster said that what is occurring in Oklahoma is a manageable problem, and Colorado provides a great example of effective management that is among the best in the nation.
“We need to establish and maintain scientifically informed and effective regulation that works with citizens and with oil-producing and water disposal industries,” he said.
“Oklahoma is now trying to put the dragon back into the cage, but there are some promising steps there as well. Regulatory actions related to the Cushing situation are hopefully a tipping point towards better regulating wastewater injection,” he continued. “There are definitely areas where you shouldn’t inject wastewater, including when you have large faults near important infrastructure. These huge facilities store up to one day’s use of oil for the entire planet.”
Oklahoma is experiencing a record-breaking year in its number of earthquakes. As of October 2015, the state already had surpassed 2014 figures, McMahon said.
She’s now conducting a detailed study of the aftershock sequence that took place
in Prague, Okla. in November 2011. “That quake, the largest in the state’s history, was felt in 17 states,” she said.
Through this research, McMahon has created a new, more precise way to detect, locate and analyze large numbers of smaller earthquakes. She teamed up on this project with U.S. Geological Survey researchers based in Golden.
“Nicole is looking at this process in unprecedented detail, and we’re getting to the point where we can begin some level of operational earthquake forecasting,” Aster said.
“This essentially allows us to better identify seismically active regions and to make statistical estimates of earthquake behavior in a manner that is a bit like what meteorologists do for weather reporting. This is a good step forward in our ability to monitor earthquakes and advance public safety.”
Aster said this type of research could ultimately have a tremendous impact in the way we monitor earthquakes near oil fields, natural fault zones, and perhaps even nuclear test sites located around the world.
In the meantime, McMahon said her family members frequently feel tremors in the Sooner State. When they text her with news of a possible quake, she verifies what took place using U.S. Geological Survey data as well as her own smarts.