TOPEKA — The Kansas Corporation Commission's conservation director Thursday said lack of information inhibited declaring a precise cause of earthquakes into Reno County far away from southern Kansas sites where a surge in seismic activity was linked to injection of oil-and-gas wastewater deep underground.

Kansas' southern tier of counties were rocked by earthquakes starting in 2013 as the oil industry increased fracking to free pockets of oil and gas from subsurface rock. Fracking wasn't the direct cause of quakes, but the high-pressure injection of millions of barrels of wastewater from the process below the surface was blamed for the sudden seismic activity.

There were 353 earthquakes in Kansas at magnitude 2.5 or greater from 2013 to 2017. That was 10 times the number documented in the previous four decades.

The KCC restricted the volume of fluids placed underground in the quake zone and the frequency of seismic activity fell in Sumner, Harper, Kingman and Sedgwick counties. In 2017, however, distant counties reported a rise in earthquakes.

KCC conservation director Ryan Hoffman told a Kansas House committee the regulatory agency was zeroing in on the Hutchinson area in Reno County because nearly 100 earthquakes of magnitude 2.0 or greater had been documented within a 15-mile radius of the city since 2016. The KCC's work delves into activity in the Arbuckle Formation, which has be a key to seismic activity in the past.

It's not clear the rise years ago in underground pressure in rock formations in Sumner County and elsewhere was directly associated with earthquakes centered many miles away, Hoffman said.

The growth in earthquakes in and around Rooks County might be attributed to natural seismic activity, he said. According to the Kansas Geological Survey, Rooks County had 87 earthquakes of at least 2.0 magnitude in 2019 — the most of any Kansas county.

"We're working on all those things. Just trying to better ask what could be happening," Hoffman said.

The Geological Survey reported wastewater injection contributed to a flurry of earthquakes felt far from injection hot spots  centered in Sumner County. Representatives of the Kansas oil and gas industry have objected to the Geological Survey's conclusion.

Gov. Laura Kelly authorized a task force that included the KCC and Kansas Department of Health and Environment to examine questions about the potential migration of earthquakes. The task force met for the first time in early January and is scheduled to report on findings in September.