The seismic sequence, including a rare “felt” quake of a magnitude 3.0 on the Richter Scale, was linked to fraccing by Hilcorp Energy Company on a well pad about a half mile from the epicentre, according to research published online today in the Bulletin of the Seismological Society of America.
One of the study’s authors, Robert Skoumal, a seismologist at the Miami University of Ohio, says that while it israre for deep fracs in shale gas extraction to cause earthquakes large enough to be felt by people on the surface, seismic monitoring advances has found the number of “felt and unfelt” earthquakes associated with fraccing has increased over the past 10 years.
“These earthquakes near Poland Township occurred in the Precambrian basement, a very old layer of rock where there are likely to be many pre-existing faults,” Skoumal said.
“This activity did not create a new fault, rather it activated one that we didn’t know about prior to the seismic activity.”
Skoumal and his fellow researchers Michael Brudzinski and Brian Currie used a technique called “template matching” to link fraccing activity on certain dates to seismic data recorded by the Earthscope Transportable Array, a network of seismic stations.
The study identified 77 deep earthquakes, with magnitudes from 1.0 to 3.0, to the fraccing done around Poland. However, only fraccing on wells in the northeast portion of Hilcorp’s shale gas operations were linked to the earthquakes, indicating where faults could be located.
“We just don’t know where all the faults are located,” Skoumal said.
“It makes sense to have close cooperation among government, industry and scientific community as hydraulic fracturing operations expand in areas where there’s the potential for unknown pre-existing faults.”
The study findings confirm two previous studies linking fraccing to hundreds of small, deep seismic events in Ohio, including 400 quakes near Canton in September and October 2013. The Ohio Department of Natural Resources also determined that the Utica Shale gas fraccing near Poland triggered seismic events and shut down work on seven of the wells.
Danielle Sumy, an earthquake researcher at the Incorporated Research Institutions for Seismology, said the science of the new report was “sound” and called the findings “quite novel”.
The novelty comes not from the fact that fraccing usually causes very small earthquakes that aren’t felt by humans, but that the magnitude 3.0 earthquake was one the largest earthquakes ever thought to be induced by fraccing in the US.
She added that the findings showed that fraccing could potentially trigger larger magnitude earthquakes than previously observed in the US, according to online portal The Verge.
