A series of small earthquakes in Lawrence County last year appear to have been linked to hydraulic fracturing operations at nearby Utica Shale wells, Pennsylvania regulators said Thursday.
The state Department of Environmental Protection said several low-magnitude earthquakes April 25 in North Beaver, Union and Mahoning townships “had a marked temporal/spatial relationship to natural gas hydraulic fracturing activities by Hilcorp Energy Co.” The department reached the conclusion after what it said was an extensive review involving the agency and outside scientific and industry partners.
DEP made the announcement in an advisory for an online event it plans to hold at 10 a.m. today to disclose details of its findings and discuss procedures it has developed to reduce seismic risk from future oil and gas operations.
A Hilcorp spokesman did not respond to a request for comment.
The U.S. Geological Survey reported sensing five minor earthquakes in Lawrence County across a 22-hour period last April with magnitudes that ranged from 1.7 to 1.9, all of which are below what humans can feel. Other seismic networks, including one overseen by Penn State researchers, registered tremors that were just larger than magnitude 2.
Seismologists have acknowledged since the first days following the small earthquakes that the depth, time and location of Hilcorp’s fracking operations at its North Beaver NC Development well pad suggested a link with the seismic events, but state officials had not broadly announced public conclusions about the events until now.
DEP officials had indicated the direction of their investigation in November at a public meeting with an oil and gas advisory board.
Because fracking forces high-pressure fluids underground to crack oil- and gas-bearing rock layers, every fracking job creates tiny tremors, or microseismic events. But in the Lawrence County case, “there was an escalation outside of that normal window of fracking microseismicity,” Seth Pelepko, a division chief in DEP’s oil and gas program, said at the November meeting.
Hilcorp picked up the growing events on its own seismic monitoring network and began to shut down its operations after the shaking reached magnitude 2, DEP officials said.
“The tell-tale sign” that the Lawrence County quakes were linked to Hilcorp’s operations was that the epicenters for two of the quakes originated “right along the lateral” leg of the company’s well bores during fracking, DEP geologist Harry Wise said at the meeting.
Researchers have linked fracking to earthquakes in several sites in eastern Ohio not far from the Lawrence County quakes, as well as in England, Canada and Oklahoma, but cases of recorded or felt earthquakes directly tied to fracking have been rare.
The Lawrence County earthquakes are the first known incidents of fracking-linked quakes in Pennsylvania.
Pennsylvania is not very seismically active, so it is unlikely that a naturally occurring earthquake would originate by coincidence at the same time and place as an active fracking operation, DEP officials said last fall.
“If you have a [seismic] event next to an operation, it would be exceptional, based on what we know in the state,” Mr. Pelepko said. “And it would probably be time to make a change in your operation based on that.”
Laura Legere: firstname.lastname@example.org.
First Published February 16, 2017 12:41 PM