Earthquakes in Pennsylvania

Last summer, with funding from the state Department of Conservation and Natural Resources, a Penn State team led by geophysicist Andrew Nyblade completed a major expansion of the Pennsylvania Seismic Monitoring Network, creating a system of 30 seismic stations spread across the Commonwealth. Located at Penn State campuses and state parks, the stations contain state-of-the-art ground motion sensors and GPS clocks. The added coverage provides for much more uniform seismic monitoring than was possible before. Nyblade spoke to David Pacchioli about the reasons behind the build-out, and the history of earthquake activity in Pennsylvania.

Why do we need an expanded seismic monitoring network in Pennsylvania?

There are three reasons. One is that there are areas of natural seismicity in Pennsylvania—one in the Lancaster-Reading area, where there have been magnitude 4 earthquakes, and the other just south of Lake Erie on the Pennsylvania-Ohio border. The largest earthquake yet recorded in Pennsylvania was the Pymatuning earthquake of 1998, just south of Erie. That was a 5.2 magnitude event. When you get to magnitude 4 and 5 events, they can be felt, and they have potential to cause damage to structures, so we need to better understand those zones of seismicity.

Then there are the reasons related to oil and gas activities—induced seismicity, possibly by fracking and more probably by wastewater disposal.

How much seismic monitoring has been done here before, and what did it find?

In 2013-14 we were able to take advantage of a temporary array of seismic stations, part of the NSF EarthScope project, to get a good baseline read on seismicity within the state. What we found was that over 99 percent of the seismic activity in the state actually comes from blasting. There is blasting in coal mines and quarries going on all the time, and some of those blasts are equivalent to magnitude 2, 2.5 earthquakes. So there’s all this background seismic activity, and we need to be able to detect and locate those events so that we can discriminate between them and anything else that might be happening.

Are fracking-related earthquakes a real possibility in Pennsylvania?

We don’t yet know for sure, but Pennsylvania may have had its first fracking-induced seismicity already. In late April [2016], we had a series of seismic events in Lawrence County, near the Ohio border, that have been correlated with a well that was being fracked there.

The bigger concern, though, is with seismicity that’s induced from wastewater disposal. The flowback waters from fracked wells, and also the wastewater that comes from conventional oil and gas wells, has to be disposed of, and a common practice is to pump it back into the ground.  There’s been a huge ramp-up of seismicity in places in Oklahoma, Kansas, Texas, and some places in Canada, and most of that is related to wastewater disposal, not to fracking itself.

Would it be possible that any induced activity would be on a par with natural earthquakes that have been recorded in the state?

Yes. In Oklahoma there have been events induced by wastewater injection that were 5.7, 5.8 magnitude. Magnitude 4s have been recorded in Arkansas and Texas related to wastewater injection. The largest fracking-related events reported so far are magnitude 4s, and those have been in Canada. So there is potential for magnitude 4s and 5s—potentially damaging earthquakes—that could be induced by either fracking or wastewater disposal.

Is there something we can do to mitigate the concern?

Absolutely. As we monitor seismicity across the state, we can detect small events when they happen and determine if they are related to fracking or to wastewater disposal, and if so notify the Department of Environmental Protection, who can then ask the well operator to shut down or take other steps. That’s one of the main purposes of the network, to be able to detect events before they get too large, so that the state authorities can take remedial action. 

Andrew Nyblade, professor of geosciences, studies seismology and tectonics in Africa, Antarctica, and North America. He is co-director of the Marcellus Center for Outreach and Research.

This interview first appeared in the Fall 2016 issue of Research/Penn State magazine.