Paul Friberg can't say whether the earthquakes that shook North Texas on Saturday, Sunday and Monday were caused by fracking. He says that there are only a handful of instances in the world in which an earthquake strong enough to be felt -- as all three of the recent quakes were -- has been definitively tied to fracking.
Friberg is a seismologist at Instrumental Software Technologies Inc. and recently co-authored a paper about hundreds of earthquakes along a previously undiscovered fault line in Ohio that were caused by fracking.
If Saturday's earthquake, which checked in at a magnitude of 3.3, was indeed caused by fracking it would be among the biggest for which the drilling was at fault. (Dale Grant a geophysicist with the U.S. Geological Survey has said earthquakes of that size are not uncommon for the area around the Barnett Shale, despite them being unheard of before fracking started in the shale.)
"If this earthquake was hydraulic fracturing induced, a Magnitude 3 is big and about as big as they get from those sorts of operations. There is report of a Magnitude 4 linked to hydraulic fracturing in Canada this year, and that would be the largest yet reported related to hydraulic fracturing operations, but that is still not a published report in a peer-reviewed journal, yet. So, it is highly unlikely to have a bigger earthquake if this is hydraulic fracturing related, but it is still possible," Friberg said via email.
Generally, he said, the earthquakes caused by fracking are very small, to the point of being imperceptible. Larger fracking-related quakes can stem from the use of wastewater disposal wells.
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"Most hydraulic fracture operations are short lived, only lasting a few weeks. So any earthquakes caused by hydraulic fracturing will go away when the operations are over. The bigger problem however has been found to be some waste water injection wells, where used hydraulic fracturing fluids or other produced waters are disposed of. Because these injection wells are disposing of larger volumes of fluid, over longer periods of time, they have more potential to intersect a fault in the basement rocks and trigger an earthquake. That said, not all disposal wells cause earthquakes either ... only a few have been linked and it is still very hard to say that a specific well caused a specific earthquake," Friberg said.
There is a wastewater disposal well near the epicenter of the Saturday night quake in Irving.
As ominous as they seem, Friberg said the earthquakes are not reason for alarm.
"Quakes caused directly by hydraulic fracturing operations are more of a nuisance than a hazard to the public," he said.