State seismic network helps tell fracking quakes from natural ones

Tools of modern earthquake science were arranged at the bottom of a 4-foot-deep hole: a Rubbermaid Brute garbage can, a stubby pedestal of fresh concrete and an olive-green cylindrical sensor about the size of a can of beans.

Up on the ledge, in a clearing behind the office at Keystone State Park in Derry Township earlier this month, Kyle Homman peered at an app on his iPod and hopped.

The earth moved ever so slightly at the Westmoreland County site and one of the newest permanent stations in Pennsylvania’s expanding earthquake monitoring network picked up the tremor.

Mr. Homman, the network’s manager, had already re-created this assemblage, alone or with help, at 19 other sites across the state. The sensor was connected to a data logger kept on the surface in a waterproof box connected to the park office by wires threaded through sealed pipes for power and internet.

Each site has been selected to fill in spots of weak coverage between the existing Pennsylvania seismic network’s 10 stations and a dozen others operated by institutions that share their data publicly.

When complete in the near future, the expanded network — funded for three years with a combined $531,000 from the state departments of Conservation and Natural Resources and Environmental Protection, and operated by Penn State University — will provide the best open and ongoing record of the state’s shaking depths that Pennsylvania has ever had.

Not a seismic hot spot

In terms of seismic intrigue, Pennsylvania has never been California. Fundamental information about why the earth sometimes shakes here has not been well defined.

“Pennsylvania has a history of small earthquakes, but we don’t understand the causes very well,” Pennsylvania state geologist Gale Blackmer said. “The more events you can map out, the better your chances are of figuring out what’s going on.”

The state agencies and their partners were also motivated to improve their ability to detect man-made earthquakes, which can be associated with oil and gas extraction as well as wastewater disposal wells, and have caused significant disruptions in other states.

As it happens, the Pennsylvania network has already picked up signals that point to both types of quakes.

In mid-April, a magnitude 2.2 earthquake near Titusville was likely a natural event, said Andrew Nyblade, a Penn State geosciences professor who championed the expanded seismic network and is the project’s principal investigator.

A week later, a series of five small tremors in Lawrence County that ranged from magnitude 1.7 to 1.9 emerged near a Utica Shale gas well that was being fracked, or hydraulically fractured — the process of high-pressure fluid injection that releases trapped oil or gas from tight rock.

The Department of Environmental Protection has not yet announced any conclusions from its ongoing investigation into the cause of the Lawrence County events, although a spokesman said its study is nearing completion.

Data generated from the state’s seismic network indicated the epicenters of the events were tectonic, or deeply seated underground, not caused by surface activity, like blasting, DEP spokesman Neil Shader said.

Tiny tremors

In the meantime, academic researchers have identified as many as a couple of hundred tiny tremors that preceded the five detectable quakes, which were themselves too small to be felt by humans. The pattern mirrors similar so-called microseismic events that were used to diagnose fracking-related earthquakes just across the border in Ohio.

Natural earthquakes in this part of the continent are usually abrupt. They tend to erupt all of a sudden and be trailed by diminishing aftershocks.

Man-made or induced earthquakes tend to emerge after a series of subtle, growing tremors as faults slip in response to pressure from injected fluids building up underground, Mr. Nyblade said.

Using a technique called template matching, researchers at Miami University in Ohio isolated the signature of the signal earthquake in the Lawrence County series and then searched seismic records for smaller matches. They found a couple of hundred that came in a pattern of bursts and pauses, seismology professor Mike Brudzinski said.

“That sort of pulsing is not something you typically see with natural seismicity,” he said.

“The signatures we’ve seen are consistent with what we’ve seen in prior hydraulic fracture seismicity cases.”

He cautioned that he has not been able to compare the timing of the seismic pulses with records detailing the precise timing of the fracking stages and he is still preparing his analysis for peer review.

Mr. Brudzinski had high praise for Pennsylvania’s expanded network of monitors, which, he said, “certainly helped in this case.”

“I think they are doing exactly the right thing to improve the seismic network in advance of getting suspicious earthquakes,” he said. “Many states have had to go the other way.”

Information for all

The completed network will be linked to a public website that should be online this summer and will be useful for researchers, companies and the generally curious.

Although it is still being designed, the site is expected to feature maps and information about the timing, location and magnitude of seismic events. It will also link to the stations’ real-time monitoring records that will be hosted and archived by the university consortium IRIS, or Incorporated Research Institutions for Seismology, which is supported by the National Science Foundation.

“The goal is to put the information out there for anyone to access on an open website in a clear and understandable fashion,” Mr. Nyblade said.

Clearer information about the geology beneath Pennsylvania could help researchers predict seismic hazards.

For example, the network’s data might help researchers delineate the boundary between the oldest layers of sedimentary rock that settled over geologic time and the basement rock below it — a line that, for now, is drawn on maps in the public domain based on limited information, Mr. Nyblade said.

That line is important because the few known cases of man-made earthquakes in the region have generally been associated with fracking in the deep Utica Shale or wastewater disposal relatively close to the basement. So defining the depth to the basement, Mr. Nyblade said, “should help in terms of understanding where areas might be more prone to fracking-induced events as the Utica is developed more extensively.”

Along with the network’s immediate monitoring and public safety applications, the project’s backers also hope to promote its value for basic scientific exploration.

Specialists can interpret what look like squiggly lines to lay people to discern information about the deep structure beneath us, and even, as Ms. Blackmer put it, “the deep, deep structure — through the whole Earth’s crust and maybe into the mantle.”

“It’s the next frontier,” she said. “Let’s go deep.”

Laura Legere:

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