March 27th, 2013 by Joshua S Hill
The linkage between wastewater injection and earthquakes seems to have been covered ad nauseum over the past few years, especially in relation to the Oklahoma earthquakes on November 6, 2011, when a 5.7 magnitude earthquake near Prague (in Oklahoma, not in Europe) was preceded by a 5.0 shock and followed by literally thousands of aftershocks.
Earthquakes in Spain have been linked to groundwater pumping from an aquifer, and reports from the Ohio Department of Natural Resources, the University of Texas, and our very own Editor in Chief Zachary Shahan also made a compelling case for the links between wastewater injection and earthquakes.
Now, a new study in the journal Geology has added its weight to the debate as to whether the Prague earthquake was wastewater induced.
For those a little on the edge of the story, wastewater injection is simply the removal of water from fossil-fuel energy production into the ground — whether for hydrofracking, which uses the pressure of the water to crack open rocks to release natural gasses, or using the water to force petroleum out of conventional oil wells. In both cases the water has to be disposed of somewhere away from drinkable and habitable water supplies, so it is often pumped underground somewhere.
For the Prague case specifically, the watery culprit was once used to extract oil from a nearby oil well and then pumped into an abandoned oil well close by.
Normally geologically sedate areas of Arkansas, Texas, Ohio, and Colorado have recently become relatively earthquake-prone, with quakes in the middle of the US jumping 11-fold over the past four years when compared to the previous three decades. The risk is such that the National Academy of Sciences in a report last year called for further research to “understand, limit and respond” to induced seismic events.
The study looked at the evidence for the Prague quake and found that as wastewater refilled now-empty oil wells the pressure to continue filling the holes with water had to be increased which caused the Wilzetta fault to jump.
When you overpressure the fault, you reduce the stress that’s pinning the fault into place and that’s when earthquakes happen,” said study coauthor Heather Savage, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory.
The amount of wastewater injected into the well was relatively small, yet it triggered a cascading series of tremors that led to the main shock, said study co-author Geoffrey Abers, also a seismologist at Lamont-Doherty. “There’s something important about getting unexpectedly large earthquakes out of small systems that we have discovered here,” he said. The observations mean that “the risk of humans inducing large earthquakes from even small injection activities is probably higher” than previously thought.
Recordings taken by lead author, University of Oklahoma seismologist Katie Keranen, showed that the fault rupture was no more than 650 feet from the active injection wells, and maybe even closer.
The Oklahoma Geological Survey is still continuing their own account of the events, and survey seismologist Austin Holland said the study showed the earthquake sequence could have been triggered by the injections. But, he said, “it is still the opinion of those at the Oklahoma Geological Survey that these earthquakes could be naturally occurring. There remain many open questions, and more scientific investigations are underway on this sequence of earthquakes and many others within the state of Oklahoma.”
Distressingly, the Wilzetta fault remains under stress and regulator’s have yet to suspect injection of water despite the cloud hanging over the recent earthquake. The study’s authors believe that water injection should be kept away from known fault locations, and that companies involved in wastewater injection should be compelled to provide accurate measurements of the amount of water that is being pumped into the ground and at what pressure. They also recommend that sub-surface monitoring of fluid pressure for earthquake warning signs. Further research is needed but at a minimum, “there should be careful monitoring in regions where you have injection wells and protocols for stopping pumping even when small earthquakes are detected,” said Abers.
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