The US Geological Survey has incorporated manmade earthquakes into its 2016 earthquake forecast for the Central and Eastern United States (CEUS), which have become increasingly common in the region in part due to oil and gas drilling activity.
Earthquake activity in the CEUS region – particularly in states like Oklahoma, Kansas, and Texas – has increased markedly, according to the USGS, in large part because of "induced seismicity." Unlike natural earthquakes, these seismic events can be attributed to human activity, and in the CEUS, that usually means wastewater disposal from oil and gas drilling.
Yet induced seismicity is such a novel issue regulators are struggling to figure out how to reduce the number of manmade quakes. States like Kansas have made some progress, but induced earthquakes are not considered in building-code maps, and nearly 8 million people live in areas that are vulnerable to that kind of activity, according to the agency's 2016 forecast.
"Earthquake rates have recently increased markedly in multiple areas of the Central and Eastern United States, especially since 2010," the report says. "Scientific studies have linked the majority of this increased activity to wastewater injection in deep disposal wells."
The drilling process leaves drilling companies with tons of briny wastewater and chemicals that come up to the surface with the oil and gas, and for decades companies have disposed of the wastewater by pumping it deep underground. In recent years, improved technology allowing companies to drill faster and wider has seen more and more wastewater pumped underground.
Near some areas of active induced earthquakes, hazard is higher than in a 2014 USGS survey by more than a factor of 3, according to the report, though that survey did not consider induced earthquakes. In some areas, previously observed induced seismicity has stopped or diminished, highlighting the challenge of linking human activity with seismic events and thus preventing them in the future.
"Uncertainties are high in this analysis, and an important topic for future research is to try to quantify and reduce these uncertainties," the report concludes.
Kansas is one state that, tentatively, suggests it may have found an answer. From 2000 to 2013 the state never saw more than four earthquakes magnitude 2.5 or greater every year, but in 2014 that number jumped to 154, including nine quakes of a magnitude 3.5 or more.
In March 2015, state regulators ordered drilling companies in some of the most vulnerable areas to dramatically reduce their wastewater injection volumes. Results have been promising in two of those areas: Harper and Sumner counties, which are in the Arbuckle Shale that straddles the Kansas-Oklahoma border.
In the 290 days before the rule went into effect, Harper and Sumner counties experienced 165 quakes, including 56 greater than magnitude 3. In the 290 days after the rule went into effect, they experienced 138 quakes, including 34 greater than magnitude 3, according to USGS data.
Across the border in Oklahoma, regulators there ordered drillers to reduce the depth of their injections, but didn’t place any limit on injection rates or volumes. There were more than 900 earthquakes magnitude 3 or higher last year, including two within eight minutes of each other this past weekend.
In January, regulators amended the order, telling some well operators to reduce their injection volumes, but capping well injections like that may only be a solution that works in the Arbuckle, experts say.
"Each state is unique and will face different challenges regarding this issue as it is developing," Ryan Hoffman – director of the Kansas Corporation Commission, the agency that issued the March 2015 order – told The Christian Science Monitor in January.
"Rather than approaching the issue on a statewide or national scale, it is important to identify areas more susceptible and take whatever actions are necessary for that specific area," he added.
Indeed, the USGS suggested in its forecast that the two hazard models they used should be updated every year based on the changing variables.
"Future hazard models could be updated every year, or even over a shorter time period, to improve the model's predictability and its usefulness to policy makers," the report says. "Varying disposal activities, policy changes, and further scientific research will change this model."
Material from The Associated Press was used in this report.