Since fracking recommenced in Lancashire there have been 17 earthquakes in nine days.
There were 18 earthquakes, but they’re very small, and earthquakes of this scale happen thousands of times in the UK each year. Fracking inherently tends to cause small earthquakes, but has occasionally been indirectly linked with larger ones as well.
“Fracking halted again in Lancashire after 17th earthquake in 9 days.”
Metro, 26 October 2018
Eighteen “seismic events” were detected near fracking sites in Lancashire in the nine days following 18th October.
Fracking was controversially resumed in Lancashire earlier this month after a seven year suspension.
The earthquakes detected were all very weak and the British Geological Survey (BGS) says earthquakes of these strengths are hardly ever felt by people and occur several thousand times in the UK each year.
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Fracking is a technique used to extract natural gas from underground shale rock. Water, sand and chemicals are injected at high pressure into underground boreholes to open up cracks in the rock. This allows trapped gas to flow out to the surface.
The BGS says: “hydraulic fracturing is generally accompanied by micro-seismicity (very small earthquakes that are too small to be felt)” as rocks are deliberately fractured and move against each other.
That sort of “micro-seismicity” has been observed at the Lancashire fracking sites. Since fracking resumed this month, the biggest earthquake measured 1.1 on the magnitude scale and the others were all below 1.
To understand how big that is, it’s important to know that magnitude is measured on what’s called a “logarithmic” scale. That means that each step up the scale indicates a ten times increase in size. For example a magnitude 2 earthquake is 10 times as large as a magnitude 1 earthquake, not twice as large.
Or to give a real world example, the San Francisco earthquake of 1906 which destroyed most of the city and killed up to 3,000 people had a magnitude of 7.9. That’s over six million times larger than the 1.1 magnitude earthquake in Blackpool.
The BGS says earthquakes with magnitudes lower than 2 are not usually felt, and if they are then by a small number of people who are near the focal point. Meanwhile earthquakes less than 1 are “hardly ever felt”.
While the BGS has observed lots of these small earthquakes in Lancashire over the past few weeks, it hasn’t observed many at other locations.
That’s not because they’re not happening though. The BGS has temporarily installed sensors which can detect extremely small seismic events in the Blackpool area, while its other sensors in the rest of the UK typically can only detect earthquakes with magnitudes of 2 or above.
It also says that it’s normal to expect several thousand small earthquakes in the UK each year that measure above 0 on the magnitude scale.
Seismology expert at the University of Southampton Dr Stephen Hicks told us that there have almost certainly been incidents when fracking triggered earthquakes in existing geological faults.
For example, before fracking was suspended in 2011, a magnitude 2.3 earthquake was detected close to a fracking site in Lancashire (though the BGS says it’s unable to say conclusively if it was caused by fracking).
But Dr Hicks said it’s difficult to predict when fracking might trigger earthquakes because existing fault lines in subterranean rock haven’t yet been completely imaged.
Correction 19 November 2018
Originally the article said that each step up the magnitude scale indicated a ten times increase in strength, when it should have said size.
Earthquake "strength" could refer to the total energy release of an earthquake, which increases by roughly a factor of 30, not ten, for each step up the magnitude scale.
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