The earthquake risk for Oklahoma and southern Kansas is expected to remain significant in 2017, threatening 3 million people with seismic events that can produce damaging shaking, according to a new U.S. Geological Survey forecast released Wednesday.
The seismic risk is forecast to be so high that the chance of damage in Oklahoma and southern Kansas is expected to be similar to that of earthquakes in California, USGS scientists writing in the journal Seismological Research Letters said Wednesday.
In 2016 alone, Oklahoma experienced several damaging earthquakes, including a magnitude 5.0 temblor in November near the central oil town of Cushing — which proclaims itself the “Pipeline Crossroads of the World” — that dislodged unreinforced bricks in chimneys and storefronts, sending them tumbling onto the sidewalks.
Oklahoma also saw the largest quake ever recorded in the state in 2016, when a magnitude 5.8 earthquake struck near Pawnee.
The earthquakes are thought to be the result of the disposal of wastewater deep underground that are a byproduct of oil extraction. Injecting the wastewater underground is not thought to trigger earthquakes everywhere it is practiced — in North Dakota, for example — but is widely believed by scientists to be a problem in Oklahoma.
According to scientists, there were only about two earthquakes a year of magnitude 2.7 or greater in Oklahoma from 1980 to 2000. But that number jumped to 2,500 in 2014 and soared to 4,000 a year later.
There has recently been a decrease in wastewater being injected deep underground, either because of regulatory actions or because oil and gas extraction has declined due to falling petroleum prices. That might be a reason for the decrease in the number of Oklahoma earthquakes last year, to 2,500.
In a statement, Mark Petersen of the USGS said the amount of injected wastewater in some areas has been reduced by up to 40% in 2016.
But the USGS report says the forecast earthquake hazard in 2017 “is still significantly elevated” compared to the seismic risk before 2009.
The Oklahoma Geological Survey’s director, Jeremy Boak, said in a statement that he expects that state directives to curtail wastewater injection rates and low oil prices “should result in further declines in the seismicity rate and limit future widespread seismic activity.”
A spokeswoman with a research and education program of the Independent Petroleum Assn. of America, Katie Brown, said in an email the reduced number of earthquakes “is a clear sign that the collaborative efforts between industry, scientists, and regulators are working.”
Accompanying the rise in Oklahoma’s earthquakes has been a significant jump in wastewater injected underground in increasingly deeper wells as oil companies have sought to extract untapped oil fields far underneath the state. Workers inject water at high pressure to break up the earth to tap into these deep oil wells, a process known as hydraulic fracturing, or fracking.
The petroleum harvest from these wells are a mix of not only oil and gas but salt water — all part of the stew of ingredients that come from the decomposed biological components of ancient oceans, said USGS research geophysicist Justin Rubinstein, deputy chief of the agency’s induced seismicity project.
Recent harvests have had a high percentage of salt water in them — requiring oil companies to deal with a significantly larger amount of wastewater than they’ve had to before. But as more wastewater has been injected deeper into the earth, underneath the ground water table, the number of earthquakes have risen in Oklahoma.
Increased fluid deep underground can change the pressures on earthquake faults in a way that essentially lubricates them, making them more likely to move and resulting in an earthquake, Rubinstein said.
