A new study connects some 400 micro-earthquakes near the town of Canton, in Harrison County, to hydraulic fracturing wells. The three wells operated from September through October 2013 in the Utica Shale. Ten of the quakes registered between magnitude 1.7 and magnitude 2.2, but the tremors were too deep to cause damage or to be easily felt by people, according to the study, published today (Oct. 14) in the journal Seismological Research Letters.
The new study is the second report this year of fracking-linked earthquakes from drilling in the Utica Shale. The shale is a rock formation that is deeper and closer than the Marcellus Shale to the crystalline basement rocks where faults are more common. In March, scientists with Ohio’s Department of Natural Resources (ODNR) shut down drilling at seven Utica Shale gas wells in Poland Township after fracking triggered two small earthquakes. The ODNR now requires monitoring of seismic activity at fracking sites near known fault lines, and reducing the flow of water if earthquakes begin to occur.
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The Harrison case is one of the few scientifically documented incidents of hydraulic fracturing causing earthquakes on a fault, said lead study author Paul Friberg, a seismologist and owner of Instrumental Software Technologies Inc. (ISTI). Harrison County is the fifth documented case in the world, Friberg said. Other locations of felt earthquakes caused by fracking include Oklahoma; the United Kingdom; British Columbia, Canada; and Ohio’s Poland Township. [7 Ways the Earth Changes in the Blink of an Eye]
Fracking involves pumping large volumes of water, sand and chemicals into underground shale or other rocks, such as coal. The pressure forces open the rocks, allowing trapped oil and gas to escape.
Within the oil and gas industry, hydraulic fracturing is known to cause earthquakes, but the tremors are usually so small that seismometers barely wiggle in response. The micro-earthquakes from fracturing rocks often register as negative magnitude 1 to negative magnitude 3. (The magnitude scale is logarithmic. On a seismogram, a wiggle of 20 millimeters, or 0.8 inches, corresponds to a magnitude 2 earthquake, and a wiggle of 0.02 millimeters is magnitude minus 1.)
“Fracking earthquakes pose no real hazard, because they are so small in the majority of cases,” Friberg told Live Science in an email interview.