You can see fracking’s impact on Earth’s surface from space | New Scientist
Fracking can lift Earth’s surface, a movement that has now been detected from space and can help predict where quakes induced by the activity are likely to strike.
This slight buckling – just 3 millimetres a year – happened when frackers injected waste water at high pressure into rocks deep underground.
The deformations were seen near the location of the biggest quake ever recorded in eastern Texas: the magnitude 4.8 Timpson earthquake in 2012, widely blamed on waste water being injected at fracking sites close to the eponymous town.
“To the best of our knowledge, it’s the best explanation and proof that injection can trigger an earthquake,” says Manoochehr Shirzaei at Arizona State University in Tempe.
Shirzaei’s team found that the geology of the zone where the water is injected can determine whether a quake is likely. They studied two pairs of fracking wells 15 kilometres apart, one to the west and one to the east of Timpson.
Surface buckling only occurred in association with the eastern wells, yet the wells to the west were the ones that probably caused the quake.
Shirzaei says the buckling happened in the east because a layer of impermeable rock beneath the injection site prevented the pressurised water from getting to quake-prone faults much further down.
Instead, the stress was relieved by the upward buckling of the rocks detectable from space. In the west, by contrast, there was no such impermeable layer, allowing the high-pressure water to reach deeper, quake-prone faults.
This means that frackers should ideally inject waste water into zones sandwiched between two impermeable layers.
“If you inject at the right depth, and it’s sealed at top and bottom, you minimise both the chance of a quake and of contamination of groundwater,” says Shirzaei. “If frackers follow this recipe we provide, they can minimise the numbers of large earthquakes they’re likely to cause.”
By combining local geological knowledge with satellite data on existing injection sites in that location, Shirzaei hopes it will be possible to more accurately predict where future injections are likely to trigger quakes. “What we propose is to help frackers minimise the risk,” he says.
Shirzaei and his colleagues have already begun analysing a magnitude 5.8 quake that struck near Pawnee, Oklahoma, earlier this month. It has been blamed on injections of waste water from nearby fracking wells, with 37 of them shut since the quake on 3 September as a precaution.
“We’re investigating, but it’s reasonable to assume the injections have something to do with it,” he says.
Shirzaei says earthquakes were almost unheard of in the US Midwest prior to the fracking boom that began around 2008. But between 2009 and 2015, there have been 1570 with magnitudes exceeding 3.
Cliff Frohlich at the University of Texas at Austin, who led another team analysing the 2012 quake, says the new research shows that checking satellite data is a promising technique for showing where induced earthquakes are possible. “But, in this case, the satellite data didn’t show effects for the wells nearest the earthquakes that probably caused the Timpson event,” he says.