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An unknown unknown

In order to secure licenses to carry out fracking in the UK, the oil and gas companies involved signed up to a tight regulatory framework.  In part, this was done to sell fracking to a highly sceptical population.  Given Britain’s long history of extractive industries poisoning land and water courses and leaving the public to pick up the cost of the clear-up, this was no doubt prudent.  The trouble was, however, that the fracking industry – whose profitability is debateable even when subject the USA’s far looser environmental standards – was unable to meet the regulatory standards that it had signed up to.

Most notable among these standards was the agreement to curtail fracking activities in the event of relatively low threshold seismic activity.  In 2011, a series of small earth tremors in Lancashire resulted in an English moratorium on fracking.  When the moratorium was lifted last year and fracking company Cuadrilla restarted its operations, it quickly triggered off another series of earth tremors; causing more shutdowns and leaving operations on hold for the time being.

While positive for the environment and for a UK government that is struggling to meet its carbon emissions targets, the Richter scale 0.5 upper limit agreed with government is extremely bad for investors who have already pumped millions of pounds into UK fracking.  And so the fracking companies – along with bought-off sections of the mainstream media – are demanding that the UK government dramatically increase the limit so that most fracking-induced earthquakes will no longer halt operations.  As industry journal Hydrocarbons Technology reported earlier this month:

“Multinational company Ineos has urged the UK Government to discontinue its ‘unworkable’ shale rules and gas fracking or risk pushing the country into an energy crisis.

“Under the existing traffic light rule, shale operators are required to stop fracking for 18 hours if seismic activity reaches a magnitude of 0.5 or higher.

“The company has called for an increase in the shale seismicity limit to a more ‘sensible’ level on the Richter scale.  To further drive its point, the company, which is a major shale gas licence acreage holder in the UK, stated that the current 0.5 level is more than 3,000 times lower than the 4.0 level adopted in the US.”

While it is true that a 0.5 earth tremor is unlikely to be noticed, and would cause far less ground movement than a lorry passing by on the road outside, the same cannot be said of earthquakes in the 4.0-5.0 range.  Just a year ago this weekend, Britain – not a seismically active region of the planet – experienced a 4.4 earthquake that caused minor damage.  My own experience (I live less than 50 miles from the epicentre) was the sensation that my house moved a foot or so sideways; I initially thought a car had crashed into the building.  As the BBC reported at the time:

“A minor earthquake with a 4.4 magnitude has affected parts of Wales and England.

“The quake was felt over all of Wales, most of western England, as far east as London and as far north as the southern edge of the Lake District, the British Geological Survey (BGS) said.”

The absence of injury or serious damage would seem to back the fracking industry’s call for an increase in the limit to the USA’s 4.0.  However, as a commenter on a Financial Times article on the subject points out, the UK and the USA are very different places:

“4 on the Richter scale might be acceptable in the USA which is a big country with a low density populous. It would be interesting to know what the average population density figures are for the fracking regions of the USA, but I would suggest that they are likely to be far lower than for the area around Blackpool, and consequently not as disruptive for those communities.”

This is where we enter the territory of unknown unknowns.  Human activity-induced earthquakes have not been the subject of much scientific investigation.  Rather, the debate about the seismic limits placed on fracking is being informed (and potentially misinformed) by research into single tectonic events.  As Cuadrilla’s 2011 and 2018 operations have shown, however, rather than single events, fracking is likely to trigger an ongoing series of small-scale earthquakes; something that is not fully understood. 

In a recent review article in Advances in Civil Engineering, Taylor et al. set out some of the known impacts of such events:

“Small magnitude (between M3 and M5), shallow (2–5 km), geoengineering-induced seismic events have demonstrated damage to many types of structures. Nowhere is this more apparent than in aseismic intraplate regions wherein damage is observed from both single and repeated small, shallow events. A series of shallow events in Alberta, Canada (largest event M4.0), caused some minor building damage. Residential damage has been observed within the Central United States, for example, the 2012 Timpson, Texas sequence (largest event of MW-RMT 4.8) and the 2013 Azel, Texas sequence (largest event M3.7). In Cherokee, Oklahoma, there were several events on February 5, 2015 (largest event of M4.2) wherein interior walls were damaged in the Alfalfa County Courthouse. In November 2014, an M4.9 event occurred in the vicinity of Milan, KS, with damage to the Harper County courthouse as well as to surrounding churches and residences; events continued through the spring of 2015 wherein new cracks generated and existing building cracks enlarged. On May 2, 2015, an M4.2 event occurred in Michigan with residential and commercial damage, for example, cracks in walls. This by no means an all-inclusive list; however, it is typical of the seemingly inconsequential damage documented from induced seismicity. Could future small magnitude-induced events affect larger and heavier structures? Quinn and Taylor showed fatigue failure potential from induced strains in earthen structures subjected to minor ground accelerations while under normal to slightly elevated service load and not necessarily limited to sudden catastrophic failure from a single large event. More importantly these damage reports indicate potentially more problematic hazards: (1) repetitive loading and (2) subsurface fatigue.”

What little evidence we do have, then, suggests that a series of relatively small earthquakes would indeed, have a cumulative impact on infrastructure.  As such, the Financial Times correspondent is correct to raise the much higher earthquake risk in a population-dense country like the UK where a large part of the housing stock is more than a century old, and where little thought would have been given to earthquake risk at the time of building.  In the vast open spaces of Texas, multiple earthquakes create less vulnerability simply because there are fewer structures to be affected.  But the risk – even at the same threshold – is multiplied in a town like Blackpool (just a few miles from Cuadrilla’s fracking well) simply because of the density of the buildings.

Thus far, the UK government (which is currently melting down over Brexit) has shown no enthusiasm for altering the regulatory framework that the fracking companies initially signed up to.  And as I have pointed out previously, even those who support fracking on energy security grounds have good reason to leave UK gas in the ground for the time being, as the world market is currently awash with cheap gas.  However, with Brexit done and dusted and the government free from previous European environmental standards, it is entirely possible that current standards will be relaxed. 

If so, Blackpool may become the first place on earth to answer – in the worst way possible – just how much damage a series of small earthquakes can cause to a built-up area.

As you made it to the end…

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