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.