Fracking for oil and natural gas, and the underground disposal of wastewater that occurs in the process, has been linked to earthquakes in recent years. Now seismologists have discovered a new twist in that relationship, finding that wastewater injection can also contribute to temblors induced remotely by faraway seismic events.
The study found that industrial wastewater disposal made certain areas more prone to seismic activity in the wake of a larger event, linking quakes near wastewater injection sites in the United States to those as far away as Japan and Chile.
"The fluids are driving the faults to their tipping point,"...
They focused on earthquakes that occurred shortly after three large quakes: an 8.8-magnitude earthquake in Chile on Feb. 27, 2010, the 9.1-magnitude event off the coast of Japan on March 11, 2011, and an 8.6-magnitude quake in Sumatra, Indonesia on April 12, 2012.
"We saw that three areas in particular have an increase in seismicity in the days following these big events," Savage explained. "These areas were in Texas, Colorado, and Oklahoma."
Most of the triggered quakes occurred in clusters and were too small for humans to notice, but others were more significant. For instance, a 4.1 magnitude triggered quake shook the town of Prague, Oklahoma about 16 hours after the 2010 quake in Chile.
One thing the affected areas in the three states all had in common was that they were located near sites where wastewater injection had been ongoing for decades.
UCSC's Brodsky called the findings by van der Elst and his colleagues "totally cool" because it means scientists can use dynamically triggered earthquakes to gauge the health of a fault to see if it's close to failure.
To be able to "probe and know what those faults are doing kilometers underground simply by watching how they react to passing seismic waves—that's new," Brodsky said.
Brodsky is the coauthor of a separate study, also appearing in this week's issue of Science, that suggests pumping water into and out of an underground reservoir to produce geothermal power can also induce earthquakes.
Consider the possibilities from the perspective of a sci-fi enthusiast. Now we have a way to assess the probability of a fault slipping. In the long term wouldn't it make sense to deliberately promote tiny triggered quakes in clusters to gradually release fault tension instead of waiting for it to buildup to destructive magnitude? If we study the cause and effect, quantify the important variables this could develop into a powerful tool of earthquake management. Instead of shutting down geothermal plants because they trigger earthquakes we could learn to manipulate the geologic "side effects" to advantage.
According to the USGS,
Seismologists have observed that for every magnitude 6 earthquake there are about 10 of magnitude 5, 100 of magnitude 4, 1,000 of magnitude 3, and so forth as the events get smaller and smaller. This sounds like a lot of small earthquakes, but there are never enough small ones to eliminate the occasional large event. It would take 32 magnitude 5's, 1000 magnitude 4's, OR 32,000 magnitude 3's to equal the energy of one magnitude 6 event. So, even though we always record many more small events than large ones, there are far too few to eliminate the need for the occasional large earthquake. As for "lubricating" faults with water or some other substance, if anything, this would have the opposite effect. Injecting high- pressure fluids deep into the ground is known to be able to trigger earthquakes—to cause them to occur sooner than would have been the case without the injection. This would be a dangerous pursuit in any populated area, as one might trigger a damaging earthquake.
The seismic attributes of an area need to be considered in evaluating the suitability for fracking - are there faults nearby, are they under tension, etc.