State scientist says recent Wichita quakes human-made, estimates how big they can get
The probability has fallen to near zero that Wichita’s recent spate of earthquakes is a natural phenomenon, the state’s top quake scientist told lawmakers on Thursday.
But while the overwhelming likelihood is that the quakes have been caused by human activity, there’s no single cause scientists can point to and say quit doing that, said Rick Miller, senior scientist in the Exploration Services Section of the Kansas Geological Survey.
“The statistics point us toward something inducing it,” Miller said. “But we haven’t found anything within our normal search areas that suggest anything that could be doing it.”
Scientists also can’t tell whether or how long east Wichita will continue to shake on a regular basis.
“If we can find what’s causing it, if there is a cause, then we can say we can stop them,” he said. “If there is no cause that we can find, or if it’s a complex system where multiple things occurred that we never can unravel, then we don’t know.”
The more quakes, the more data is generated and the higher the probability of human causation, Miller told the House Utilities Committee on Thursday.
When the first quake hit last December, the probability was 99.9 percent that it was a natural occurrence.
When the second came about 10 days later, that probability dropped to 3.2%. “By the time you had the fifth event, which was the beginning of March, statistically, there’s no probability for that to be natural,” Miller said.
But on the upside, the scientists believe there’s an upper limit on how how hard Wichita could shake — magnitude 4.5, Miller said. But even that comes with a caveat.
“If we get more magnitude 3s, more magnitude 4s, then that may change that number,” Miller said. “But right now the data we do have says that it should not get above 4.5 and more than likely 4.2.”
That’s not a level high enough to do much, if any, structural damage to homes and businesses, he said.
Basically, earthquakes below 5.0 mainly will cause cosmetic damage,” he said. “It will cause pictures to fall from the walls, Grandma’s tea set to fall off the counter, it will do damage to things that aren’t secured.”
While the cause of the Wichita quakes is still a bit of a mystery, the data points to a rise in deep subsurface fluid pressure related to oil and gas production.
In Kansas, producers get about 18 barrels of salt water coming up with each barrel of oil. That water, too polluted for surface disposal, is poured back underground through deep injection wells.
That creates pressure deep underground that can cause faults to slip, causing earthquakes.
Ryan Hoffman, director of the Kansas Corporation Commission division that regulates oil and gas production, said Kansas has 16,457 wastewater disposal wells and the state ranks No. 3 in the nation for subsurface disposal.
Roughly 2,500 of those are very deep, drilled into the Arbuckle Formation that underlies oil-producing regions of Kansas and Oklahoma.
“That’s generally what we’re looking at when we’re talking about induced seismicity,” he said.
While most of the disposal in Kansas takes place well south of Wichita, disposal can increase subsurface pressure across a broad area.
The fault causing all the shaking in east Wichita may actually be a T intersection of two faults, Miller said. But generally, faults only reveal themselves when they slip and cause an earthquake.
“The pressure in the Sedgwick Basin (which underlies Wichita) is likely exceeding triggering thresholds, which means that this may not be the last place that we see clusters like this of earthquakes go off where we’ve not seen them recently, or at a rate that we’ve not recently seen,” he said.
And the oil and gas industry is not the only one using underground disposal. They’re also used for disposal of tainted water from the salt and chemical industries, Miller said.
Those disposal wells, though they operated problem free for decades, could be a factor now, he said.
“That’s because we believe that a lot of the area has reached a pressure where . . . the cumulative injection has pushed it to where things that we used to be able to do routinely as part of industrial processes now may trigger earthquakes,” he said.
The Arbuckle Formation will drain that pressure over time, but it’s a slow process, Miller said.
The challenge for scientists and regulators now is to try to reach a balance point and determine how much waste water the Arbuckle Formation can handle while relieving the pressure that’s causing quakes, he said.
This story was originally published March 25, 2021 at 1:40 PM.
