Killer tornadoes, sizzling summers, treacherous ice storms. Barbara Scott was prepared for all that and more when she moved from Denver to Bluff City, Kan., a half dozen years ago. But earthquakes? In Kansas?
"It's like the earth just rolled under my house, raised it up and lowered it down," she said of the quake that struck last month between Bluff City and Caldwell. Further rattling Scott was the possibility that the earthquake was man-made, a byproduct of our lust for energy.
"We thought it might be the fracking," she said. "We have so much of that going on down here."
Kansas is one of five states least likely to experience earthquake damage, state officials say. The worst on record was of 5.5 magnitude in 1867 near Manhattan.
Then last fall, a swarm of tremors shook south-central Kansas sporadically over a couple of months. The culmination was a 3.8-magnitude quake on Dec. 16 that rattled windows, cracked walls and shook furniture in Sumner and Harper counties along the Kansas-Oklahoma border.
There were no injuries or reports of major damage. But the December temblor and the smaller ones leading up to it startled flatlanders unaccustomed to the kind of tremors Californians might shrug off. "It shook the house and rattled the windows," Bluff City resident Chris Garancosky said of the first quake she felt, on Sept. 9. "I thought somebody's propane tank had blown up."
Was it a fluke of nature, the earth shaking off pent-up tectonic pressure that had been building over centuries? Or might it have been yet more evidence of a phenomenon that scientists believe is on the rise throughout the nation's midsection?
That would be earthquakes with links to hydraulic fracking, the process of flushing hard-to-get oil and gas from porous, underground rock formations by fracturing them with a high-pressure mixture of water, chemicals and sand.
Fracking itself is not thought to cause quakes that people can feel. But scientists and the energy industry do agree that seismic activity can be induced when millions of gallons of wastewater from hydraulic fracturing operations are injected into the kind of disposal wells that are being used by oil and gas companies in the Bluff City area.
"I think the sense at this point," said Rex Buchanan, acting director of the Kansas Geological Survey, "is there's a reasonable chance that (the Dec. 16 temblor) was an induced earthquake."
Buchanan's agency and the Kansas Corporation Commission have yet to determine what caused the Dec. 16 quake.
One part of their investigation will be to learn how much wastewater was injected into the disposal wells nearest the quake's epicenter. Four companies have wells in that area, commission spokesman Jesse Borjon said.
Scientists have long known that injecting fluids deep into the earth can trigger earthquakes.
"There's really no doubt in the credible scientific community about that connection," said Joe Spease, chairman of the hydraulic fracturing committee at the Kansas Sierra Club.
But it's difficult to prove that a specific quake was caused by injecting fluid into a specific well, and overall the risks of damage by earthquakes are low, according to independent experts and the energy industry.
"Only a small fraction of the thousands of injection wells that exist have been tied to seismic events of notice to the public," said Dana Bohan at Energy in Depth, the research arm of the Independent Petroleum Association of America.
Still, scientists at the U.S. Geological Survey think that the frequency of earthquakes increases when wastewater floods fault zones, causing pieces of Earth's fractured crust to slip more often than they might otherwise.
The USGS points to a steep increase in the number of earthquakes in the last few years in regions of the country where oil and gas production through fracking has ramped up.
From 2010 to 2012, there were more than 300 earthquakes with a magnitude of 3 or above in the central and eastern United States. Compare that with 21 per year on average from 1967 to 2000, after which the number began to creep up.
Many of those recent quakes have occurred in Oklahoma, where a fracking boom is underway. The most powerful was a 5.6-magnitude quake centered near Prague, Okla., on Nov. 5, 2011, that destroyed 14 homes, injured two people and was felt in Kansas City and in parts of at least 17 states.