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.
Written by Chloe Marie - Research Fellow
May 31, 2016
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