Written by Chloe Marie – Research Fellow
The state of Pennsylvania is not known to be located in a region subject to significant seismic activity, although it does contain two active seismic zones – the Lancaster Seismic Zone in southeastern Pennsylvania and the Ramapo fault running through southeastern New York to eastern Pennsylvania. Historic earthquake epicenters in Pennsylvania generally have been located in Berks, Bucks, Lehigh, and Lancaster Counties and have been low in intensity. The largest earthquake recorded in the state, a 5.2 magnitude seismic event, occurred in September 1998 near the Pymatuning Reservoir in northwestern Pennsylvania.
On April 25, 2016, however, the Pennsylvania State Seismic Network (PASeis), the Ohio Seismic Network (OhioSeis) and the Lamont-Doherty Cooperative Seismic Network (LCSN) registered four small-scale earthquakes in the vicinity of Mahoning, North Beaver and Union Townships, Lawrence County, ranging from a magnitude of 1.8 to 2.3. These seismic events quickly caught the attention of the Pennsylvania state officials who then examined any potential relationship between this recent seismic activity and nearby shale gas wells. The earthquake epicenters were identified to be located within 5 miles of a single well pad – the North Beaver NC 7H – comprised of four hydraulically fractured wells operated by Hilcorp Energy Co. The North Beaver NC 7H well is located in the Utica Shale producing formation, and production activities started on March 30, 2016. Consequently, the Pennsylvania Department of Environmental Protection (DEP) called for an immediate investigation to ascertain the cause of the seismic events.
In January 2017, the DEP issued a report reviewing the seismic events in Lawrence County and concluded that “although there is no definitive geologic association of events at this time, there is a marked temporal/spatial relationship between fracking/stimulation activities at the North Beaver NC Development well site and the seismic events on April 26, 2016.”
In reaching this conclusion, DEP compared the April 2016 seismic events with seismic activity that occurred in the Poland Township area, Mahoning County, Ohio in March 2014. At that time, the Ohio Department of Natural Resources reported a series of five earthquakes ranging from a magnitude of 2.1 to 3, and it was suggested that Hilcorp’s hydraulic fracturing activities in the Poland Township area induced those seismic events. In their report on the Lawrence County events, DEP found that “similarities between the events in Ohio and Pennsylvania include temporal and spatial relationships with active fracking/stimulation activities at a nearby well pad, fracking/stimulation activities associated with Utica Shale Formation wellbores and seismic activities for both events located vertically within or near the Utica Shale Formation to a shallow depth within the crystalline basement rock.”
Based upon their investigation, DEP developed a series of recommendations to monitor and respond appropriately to potential future seismic activity associated with hydraulically fractured wells within Mahoning, North Beaver and Union Townships. Among the main recommendations, DEP suggests that the well operator pursues its earthquake monitoring plan within the townships mentioned above as well as report any seismic activity in connection with its shale gas activities.