Feb. 21 (UPI) -- Seismographs have documented a significant increase in earthquakes in southern Kansas over the last five years, and the latest research suggests the oil and gas industry's activity tied to hydraulic fracturing is to blame.
Prior to 2012, no documented magnitude 4 or greater earthquake had shaken southern Kansas. Between 2012 and 2016, as oil and gas activity increased, seismographs registered six such earthquakes.
To better understand the link between seismic activity and hydraulic fracturing, researchers with the U.S. Geological Survey analyzed 6,845 earthquakes that shook Harper and Sumner counties, home to the newest wave of oil and gas exploration.
Hydraulic fracturing involves the injection of high-pressure fluids deep into rock, most commonly shale, in order to trigger the release of oil and gas trapped between the rock layers. Often, wastewater leftover from the activity is treated and then injected back into the ground.
While researchers say the earthquakes are not linked specifically to hydraulic fracturing, wastewater injection -- an activity that follows fracturing -- may be linked to them. When scientists compared the timeline of seismic activity with the schedule of wastewater injection, they found a strong correlation between the two.
Their data showed an increased in wastewater injection and seismic activity was followed by a decrease in both in 2015. A drop in oil and gas prices, combined with new regulations designed to limit wastewater injections, likely precipitated a downturn in hydraulic fracturing activity, explaining the drop-off in the occurrence of earthquakes.
Though wastewater injections have slowed, scientists say it's possible earthquakes could continue in areas where the injection of fluids have altered the natural pressure in the underlying bedrock.
"It's hard to say how long it's going to last given that what we're looking at in Kansas is a much higher rate of injection than in the places where seismicity slowed quickly, and many, many more wells," USGS researcher Justin Rubinstein said in a news release. "If they shut off all the injection, the decay could still take years, just because there's been such a dramatic change in the regional pressure field."
Rubinstein and his colleagues published their analysis this week in the journal Bulletin of the Seismological Society of America.