Tuesday, May 31, 2016

Induced Seismicity Update – Seismicity in Pennsylvania

Historically, the state of Pennsylvania has not been known as a high-risk seismic hazard zone despite lying on the Ramapo fault system that goes from southeastern New York to eastern Pennsylvania. Pennsylvania, however, has experienced few seismic events that show a potential for large damages.

The largest and most recent earthquake in Pennsylvania was recorded on September 25, 1998, in northwestern Pennsylvania, near the Pymatuning Reservoir. The earthquake was 5.2 in magnitude and was also felt in Ohio and New York. Another swarm of earthquakes was recorded on January 16, 1994, in Wyomissing, Berks County. Two earthquakes with respective magnitudes of 4.0 and 4.6 hit Wyomissing within minutes of each other causing only little damage. An older earthquake event of magnitude 3 occurred near Centre Hall on August 15, 1991. The other recorded earthquakes in Pennsylvania were low in intensity, and most of them were reported in the eastern and northwestern areas of the state.

On April 25, 2016, a small-scale seismic event, however, caught the attention of the Pennsylvania state officials. The U.S. Geological Survey recorded an earthquake of magnitude 1.9 on April 25, 2016, in Mahoning Township, Lawrence County – which earthquake occurred near active natural gas wells. The causes and consequences of induced seismicity from wastewater injection wells and hydraulic fracturing have already been considered by many natural gas producing states, such as Texas and Oklahoma, where increased seismic events have been witnessed in the past few years. Multiple studies have concluded that hydraulically fractured and injection wells represent the most probable cause of recent earthquake activities. Following the most recent seismic activity, Pennsylvania state officials started investigating a potential link with the M1.9 earthquake.

This investigation, however, is a continuation of existing research – seismicity in Pennsylvania has been monitored since 2006 thanks to the joint effort of the Pennsylvania Department of Conservation and Natural Resources (DCNR), the Pennsylvania Geological Survey, and Penn State University. Together, they developed a seismic network called PASEIS. The PASEIS network has been designed for detecting and locating earthquakes of magnitude 2 or larger. In September 2015, the Pennsylvania Department of Environmental Protection joined the monitoring effort and, together the DCNR provided $531,000 in funding to support the seismic network for a period of three years. Starting with 6 permanent monitoring stations in 2006, the network of stations continually increased and, by the summer 2016, will include 42 high quality-monitoring stations.

On May 19, 2016, the Penn State Extension hosted a webinar addressing Dr. Andrew Nyblade’s research on seismic activity as part of the DCNR and DEP monitoring program. Dr. Andrew Nyblade, from the Department of Geosciences in Penn State, discussed the seismic network expansion but also provided an overview of his findings concerning the correlation between seismic activity and the oil and gas, and mining industries. According to him, from 2013 to 2014, 1117 seismic events can be related to mine or quarry blasts, 165 seismic events could be related to these blasts, while the cause of 11 seismic events are not mining-related. As for these 11 seismic events, Dr. Nyblade found that “no correlation has been found with either injection wells or fracked wells” and, thus, they should be considered as tectonic earthquakes.

Concerning, however, the recorded M1.9 earthquake in Mahoning County, Dr. Nyblade did not negate the possible link with hydraulically fractured wells in the area but maintained that a “whole work” needs to be done before coming to any conclusions.

PASEIS Network data are available on the Incorporated Research Institutions for Seismology’s (IRIS) official website and a PASEIS website will be coming soon providing station information and maps as well as seismic event information from the 42 stations. Additional information on the Central and Eastern United States Seismic Network can be found here and further information on earthquakes in Pennsylvania are available on the Pennsylvania DCNR’s official website.

The recorded Penn State Extension’s webinar is available here.

Written by Chloe Marie - Research Fellow
May 31, 2016

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