WICHITA, Kan. — The largest recorded earthquake in Kansas history was likely the result of wastewater injected into the ground by one or two nearby wells, according to a new study from the U.S. Geological Survey found.
The 4.9 magnitude earthquake happened in November 2014 about 40 miles southwest of Wichita.
The USGS report, which will be published in Seismological Research Letters in November, shows scientists believe the earthquake was caused by wastewater injection for several reasons, including that there hadn’t previously been similar earthquakes in the area and the earthquake activity started after the amount of water injected in the wells increased.
USGS geologist George Choy said it’s hard for scientists to predict high-magnitude earthquakes ahead of time because there isn’t a lot of historical data on earthquakes smaller than 3.5, the Wichita Eagle reported (http://bit.ly/2efBLe2 ). This resulted in scientists being unable to tell whether smaller earthquakes were natural or induced.
Before 2014, there had been fewer than one earthquake per year. In 2014, there were more than 125 earthquakes at a 2.5 magnitude or higher.
“Some things you can’t recognize until hindsight,” Choy said.
Since the 4.9 earthquake, the USGS has increased the number of seismic stations in the area from five to eight and the state of Kansas added six more.
Aftershocks usually occur in adjacent rock that was dislodged by the original earthquake. By mapping these aftershocks, scientists were able to figure out the size, shape and location of the large earthquake.
One of the two wells operated by SandRidge Energy is still injecting water at the same level as when the earthquake occurred.
“If the well is in the right place next to a fault and the fault is oriented the right way, a little change in stress could cause (an earthquake) to occur,” Choy said.
Information from: The Wichita (Kan.) Eagle, http://www.kansas.com