Earthquakes in Oklahoma are down more than 50 percent this year after regulators' actions to limit wastewater injection, but that doesn’t mean we’re out of the woods.
A magnitude 5.3 earthquake rattled Denver in 1967, two years after underground waste injection from chemical weapons manufacturing stopped.
The main culprit in Oklahoma's rapid uptick in earthquakes earlier this decade was oil and gas wastewater disposal where fluids were pumped deep into the ground. OU assistant professor and induced seismicity expert Xiaowei Chen said limiting the depth of disposal wells would help, considering the rock layer all that brackish water is going into touches a deeper one where most earthquakes occur.
"The Arbuckle Formation was previously chosen because it has high permeability and takes a lot of water, so it’s easy to inject. But what happens is it’s kind of so close to the basement interface, that’s a little bit dangerous," Chen said.
The Oklahoma Corporation Commission has limited injection volumes and rates in some areas, which Chen said has helped.
"But the next part is trying to [find] some better ways to detect the faults in the basement. It’s a little bit more challenging than detecting faults in the sediment, but we need to work on that," Chen said.
Most earthquakes caused by wastewater disposal have been in previously undetected faults in the basement layer of rock. Mapping its faults could help regulators see where further limits on wastewater disposal may be needed to keep faults from slipping.
State and local officials should be taking steps now to mitigate future damaging earthquakes, like taking stock of old buildings.
"The Cushing area, it has some collapsing. So, you want to check the building code for some of the historic buildings," Chen said. "And some areas, if you have liquefaction risk, you want to check those areas as well."
Liquefaction is when stress like an earthquake causes seemingly solid ground to behave like a liquid, causing greater damage.
