Pennsylvania State Seismic Network sees activity underground

A map of the stations used by PASEIS to collect seismic data. Red triangles indicate stations operated and maintained by the PASEIS network, and blue triangles indicate stations operated by other universities, companies and government entities.   Credit: PASEISAll Rights Reserved.

UNIVERSITY PARK, Pa. — Pennsylvania may not be famous for its earthquakes like some other states, but seismic events happen every week at quarries and other mining areas, as does the occasional earthquake. When a seismic event occurs in the commonwealth, the Pennsylvania State Seismic Network (PASEIS) is the first to know.

The network is a collaborative monitoring effort between Penn State, the Bureau of Geological Survey in the Department of Conservation and Natural Resources (DCNR), and the Pennsylvania Department of Environmental Protection (DEP). PASEIS uses data from 71 stations within and surrounding Pennsylvania for monitoring purposes.

“There’s a lot of controlled, DEP-regulated blasting from quarries and coal mines, so every week we detect and locate explosions from mining activity,” said Andrew Nyblade, head of the Department of Geosciences and co-director of Penn State’s Marcellus Center for Outreach and Research (MCOR), which supports PASEIS. “Other man-made and natural processes also occasionally produce earthquakes. Although most are small, we can detect and locate them in near real time.”

Earthquakes are most likely to occur in northwestern and southeastern Pennsylvania. The latest one, a magnitude 1.3 that could only be felt by seismometers, happened near Lancaster this past October. The state has not experienced a sizeable event since the magnitude 5.2 Pymatuning earthquake in September 1998.

Four stations must record a seismic event to locate it, said Kyle Homman, PASEIS seismic network manager and a doctoral candidate at Penn State. Homman maintains and operates 37 stations across the state and pulls data from 34 stations operated by other universities, companies or government entities. Stations consist of computers and seismometers that can detect and locate all magnitude 2 and stronger events as well as many smaller events.

A seismometer sits on a concrete slab belowground. The network of seismometers used by PASEIS can detect and locate all magnitude 2 and stronger seismic events as well as many smaller events.  Credit: Kyle HommanAll Rights Reserved.

“Pennsylvania has always had small earthquakes, but we still don’t understand exactly why they are happening,” said State Geologist Gale Blackmer, director of the DCNR Bureau of Geological Survey. “It’s tectonic forces of some sort, but exactly what is driving them we don’t quite understand.”

Most earthquakes in Pennsylvania are so small — in the magnitude 2s or lower — that they go undetected by humans unless they occur close to the surface. Blackmer said this highlights the importance of PASEIS.

“If you’re in a place where you cannot feel many of the earthquakes, then you need the network to pick them up,” she said. “It helps us better understand geologically and tectonically what’s happening here and what kind of activity we have the potential for.”

Induced seismicity, or earthquakes caused by human activity, is a concern nationwide and one that scientists and government agencies are also using PASEIS to address. Although records of induced seismicity span decades, recent concerns have surfaced in association with hydraulic fracturing and wastewater disposal related to the oil and gas industry, Nyblade said.

Hydraulic fracturing, or fracking, and wastewater disposal add new stresses to rock deep underground. These stresses can trigger movement on nearby faults, causing seismic activity, according to Nyblade.

The number of seismic events caused by oil and gas industry activities has increased in many states, including Oklahoma, Texas, Kansas, Colorado and Ohio. In some cases, fracking activities have produced magnitude 4 or 5 earthquakes, large enough to cause structural damage, he said.

Pennsylvania has only experienced one fracking-induced event, which occurred in April 2016 along the Ohio border. Fracking activity there caused five tremors of magnitudes measuring between 1.8 and 2.3, which do not create enough ground motion to cause any structural damage. Only seismometers deployed onsite by the well operator and those close by in the PASEIS network detected the event. If detected at all by humans, the tremors would have caused a slight shaking like that felt when a heavy truck passes by a house, Blackmer said.

A seismic station located in a Pennsylvania state park. PASEIS uses data from 71 stations within and surrounding Pennsylvania for monitoring purposes. Credit: Kyle HommanAll Rights Reserved.

Induced earthquakes usually start off small — magnitude 0 and 1 — and become more powerful as the pressure from fracking and wastewater disposal builds over time with continued activity, according to Nyblade.

“By monitoring, we can catch earthquakes when they’re small,” he said. “If we think any of these events may be related to oil and gas activity, we report it immediately to DEP.”

The DEP then looks at the location of oil and gas activity and its proximity to the seismic activity to determine if humans triggered the event. If necessary, the agency can tell oil and gas drillers to take remedial action, like suspending fracking activity or reducing fracking pressures.

“The PASEIS network is not only contributing to important research, it has helped DEP’s oil and gas regulatory program establish a way to detect very low-threshold seismic events throughout Pennsylvania and conduct the necessary follow-up investigations expeditiously,” said Seth Pelepko, an environmental program manager at DEP. “Although the risks for induced seismicity related to oil and gas activities have proven to be very low in the commonwealth, the network is providing another valuable tool for regulators and has helped the agency forge a valuable partnership with the expertise available through Penn State and DCNR’s Geological Survey.”

The PASEIS website lists every seismic event recorded in Pennsylvania since September 2016. Users can download the data from the website and register to receive seismic notifications. 

Last Updated November 11, 2019