Two small earthquakes that shook the Lancashire coast of northwest England and the nearby city of Blackpool earlier this year were probably caused by hydraulic fracturing, or fracking—a shale gas extraction technique that was being used nearby to explore its shale gas wells—according to a report released today. The energy company Cuadrilla Resources had begun an experimental drilling operation half a kilometer from the quakes' epicenter in March.
Fracking has caused concerns in some countries over its potential health and environmental impact—critics accuse it of contaminating drinking water with gas and the chemicals used for extraction—and it is banned in some countries and some U.S. states. Cuadrilla's is the first fracking operation conducted in the United Kingdom.
After geologists pointed the finger at Cuadrilla as the possible cause of the quakes, it commissioned independent experts to prepare a report on the topic. Entitled Geomechanical Study of Bowland Shale Seismicity, it has concluded that it is "highly probable" that the quakes were triggered by Cuadrilla's fracking: high pressure injection of fluids into rocks in order to fracture them and release shale gas. But the quakes were a fluke, the report continues, as the geology of the region was highly unusual to begin with.
Seismologist Brian Baptie of the British Geological Survey, which was not involved in the report, says this is the first time hydraulic fracturing has been shown to cause earthquakes, although it is not entirely surprising. Injection of fluid waste from shale gas and oil drilling has caused small quakes in the past. Fluid injection, he explains, creates small fissures in the rocks that allow them to slide more easily past each other, "lubricating" them in a sense. In the case of the Cuadrilla site, the report stated, this occurred near an already-stressed fault. The fluid spread over a period of 10 hours after injection and caused the quakes.
Following the magnitude 2.3 quake on 1 April and a 1.5-magnitude quake on 27 May, Cuadrilla voluntarily suspended drilling and fracking operations on 31 May. Drilling resumed, although it is shut down today due to activists who climbed the drilling towers in Lancashire to highlight fears prior to a fracking conference in London. Whether fracking will continue at the site is to be determined: Cuadrilla spokesperson Stephen Smith says that while the company could voluntarily resume at any time, they're currently awaiting reaction to the report and will work in concert with government recommendations.
It's unlikely, the report concluded, that any quake caused by this combination of geological factors could exceed magnitude 3—too small to cause any real damage. But because the fractures are relatively shallow, Baptie says, quakes of this magnitude could cause objects to slide around on shelves and cause alarm. "If quakes are in the same place and you're generating them on a routine basis, it starts to raise questions," he says. The report suggested a "traffic light" system for Cuadrilla to monitor Earth shaking in the future.
The report is now entering peer review. "We want it to subjected to maximum scrutiny; it's not in Cuadrilla's interest to discover a problem down the road," Smith says.
Correction: This item has been corrected to reflect that the Lancashire coast of England is in the northwest, not the northeast.