Risks of Raising Red Traffic Light Limit

Traffic Light System

Concerted efforts are being made by fracking operators and ‘geoscientists’ to persuade the government to increase the red traffic light limit from 0.5M to 1.5M. The Times newspaper recently published a letter by 49 ‘geoscientists’ urging the government to commission an urgent review of the fracking earthquake limit, recommending this be raised to allow the industry to expand. However, as revealed by Channel 4 News, many of these ‘geoscientists’ have direct connections to the oil and gas industry.

Current Oil and Gas Authority guidelines state that upon detection of an earth tremor of magnitude 0.5 the “…Operator[s] must suspend injection, reduce pressure and monitor seismicity and ground motion for any further events before potentially resuming.” When a seismic event of this magnitude occurs, fracking operations must cease for 18 hours while the well is flushed out and its integrity checked.

The main arguments being used to raise this limit to magnitude 1.5 are that:

  • the current red-light limit prevents effective fracturing and gas release
  • higher limits work satisfactorily in other countries, and other UK industries
  • the proposed level cannot be felt on the surface and causes no damage.

The responsible Minister (Claire Perry) recently said that she is resisting the change and has no plans to implement it. Yet six months ago she wrote to a fellow MP saying “that the monitoring system was set at an explicitly cautious level…. (and) as we gain experience in applying these measures, the trigger levels can be adjusted upwards without compromising the effectiveness of the controls.”

Seismic events occur when fault lines are lubricated, and plates slip. In this context, opponents of fracking point out that the UK has 400 times as many fault lines as the USA. Furthermore, as the UK is far more densely populated, fracking wells will inevitably be sited much closer to housing areas. They are also concerned that fracking operators’ surveys fail to pick up small fault lines, and that they are permitted to frack too close to detected faults.

Fracking opponents argue that the Preese Hall experience shows the risk of increasing the traffic light limit. The well was sunk 200 metres away from a small (unidentified) fault line. Fracking caused 58 earthquakes between March and May 2011 (de Pater and Baish 2011), the largest being 2.3M on the 1st April and the last being 1.5M on the 27th May. This latter event deformed the bottom 170 metres of the well (making it ovoid instead of round).

Operations were suspended and the well was plugged with concrete in 2013 and abandoned, but had to be replugged two years later. This reflects concerns that disused steel casings are liable to rot over time, and the concrete linings shrink and crack. These events could provide a potential upward conduit for fugitive emissions of released but unrecovered gas and fluid, contaminating groundwater resources and the surrounding land surface.

Operators have clearly been using low hydraulic pressure in order to try to comply with the current red traffic light – yet by so doing have inadvertently triggered seismic events well above this level. Lifting the limit will enable them to apply greater hydraulic pressure in order to release the gas – but risks triggering seismic events on a much larger scale than previously encountered in the UK due to Fracking.


Channel 4 News 15 February 2019

de Pater, C.J. and Baisch, S. (2011) Geomechanical Study of Bowland Shale Seismicity: Synthesis Report 

Refracktion (2019) Don’t Mess with the Traffic Light System

The Times Newspaper 9 February 2019