For the second time in four days, fracking company Cuadrilla halted and restarted its fracking activities at its Preston New Road site in Lancashire because of seismic activity, leading to many “earthquake” headlines in the media.

But who decides when fracking needs to stop and can be restarted? DeSmog UK unpacks the monitoring and real-time decision-making process behind fracking.

The process is based on the company monitoring, reporting and assessing the cause and size of the tremors and is overseen by the Oil and Gas Authority. However, it remains unclear how or if a seismic event could lead to halting all fracking activity, as it did in 2011.

‘Earthquakes’

In the fortnight since Cuadrilla began its fracking operations at the site on the October 15, the British Geological Survey recorded 26 small seismic events in the Blackpool area — including three events above the 0.5ML (local magnitude) threshold above which fracking activities must be suspended.

The largest tremor detected by the British Geological Survey took place on October 29 around 11.30am and was of magnitude 1.1ML on the Richter scale.

In a statement, Cuadrilla confirmed that it had suspended its fracking activities for 18 hours while seismic activity continued to be monitored by the company and the Oil and Gas Authority.

On October 26 and 27, two other seismic events were recorded at 0.8ML — also above the 0.5ML threshold.

While regular seismic activity has taken place around the Blackpool area since fracking began, these small tremors remain of low intensity and are usually not felt by people. Large seismic events induced by hydraulic fracturing are generally rare.

However, because people cannot feel such seismic events does not mean they should be ignored. And the Oil and Gas Authority (OGA), which regulates onshore hydraulic fracturing operations, is responsible for managing the risks linked to seismic activity.

In the US, scientific studies have shown the link between fracking activities and an increase in seismic activity. In the states of Texas, Oklahoma and Ohio, hydraulic fracturing and the use of fracking wastewater disposal injection has been repeatedly found as the primary cause for the increasing frequency and intensity of earthquakes.

In Texas, just 13 percent of earthquakes larger than 3ML since 1975 were the result of natural causes alone, according to a paper in the journal Seismological Research Letters. In Oklahoma, the US Geological Survey estimated a 5.5ML-or-greater quake was potentially due to fracking operations.

What happens when a tremor is recorded?

Before fracking can begin, companies need to present an hydraulic fracturing plan that has to be reviewed and agreed by the OGA.

The plan would typically ensure the company monitors seismic activities at the site and that it operates a real-time ‘traffic light’ system so that any operations can be quickly paused and reviewed if unexpected levels of seismic activity is detected.

The company is also expected to do additional monitoring closer to homes and other building structures near the site. This Hydraulic Fracture Plan (HFP) provides detail of what needs to happen in response to seismic activity and has to be agreed by the OGA and the Environmental Agency

Seismic events of up 0.5ML are considered amber on the traffic light scale, with the company able to continue its fracking operations “with caution, possibly at reduced rates” and with intensified seismic monitoring.

The OGA considers this to be “far below what would cause a perceptible event at the surface but is greater than the level expected to be generated by the fracturing of the rock itself”.

Image credit: The traffic light system/Oil and Gas Authority 

A tremor above 0.5ML while fracking is taking place constitutes a “red light” and the fracking company must suspend its activities immediately and for 18 hours for further monitoring of seismicity to take place.

In its statement confirming the suspension of activities on October 29, Cuadrilla said that the 1.1ML earthquake was “classed as a ‘red’ event as part of the traffic light system operated by the OGA” but added “as we have said many times this level is way below anything that can be felt at surface and a very long way from anything that would cause damage or harm.”

Fracturing activities are suspended only if the tremor was recorded at the time hydraulic fracturing is taking place.

Following the 0.8ML tremor on October 27, Cuadrilla said that the seismic event was “not a red incident” under the traffic light system because the company was “not pumping fracturing liquid as part of our hydraulic fracturing operations at the time”.

If activities are suspended, the company has to determine whether the seismicity was natural or induced and act according to the agreed hydraulic fracture plan. Ground motion also has to be assessed to identify potential damage to nearby buildings.

If the assessment confirms the assumptions and predictions set out in the plan, the company is allowed to resume operations subject to any mitigation or other measures it has to take according to what has been agreed with the OGA and the Environment Agency.

The entire process is overseen by the OGA.

Fracking tremors in context

Fracking requires the injection of high pressure fluids and chemicals into the rock to crack it open and release shale gas. The cracks grow as a result of tiny seismic events and allow the trapped gas to be extracted. These seismic events are usually very small in scale.

The injected fluids in the rock can also affect pre-existing cracks and faults in the rock. Any seismic activity that results from this is known as a triggered event.

In 2011, a 2.3ML earthquake, considered to be a triggered event led to the halting of all fracking activities. DeSmog UK is still waiting for the OGA to clarify what intensity of tremor could lead to a similar decision being made in today’s circumstances.

The British Geological Survey (BGS) says that fracking is generally accompanied by microseismicity, which it describes as “very small earthquakes that are too small to be felt”.

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According to BGS, earthquakes with magnitude less than 2ML are not usually felt by people and earthquakes with magnitudes under 1ML are hardly ever felt.

The BGS adds that on average there are around 20 to 30 earthquakes with a magnitude of 2ML in the UK or across its immediate offshore area every year.

“That means we should expect several hundred earthquakes with a magnitude of 1.0ML or above and several thousand with a magnitude of 0ML or above,” it said.

A spokeswoman for the BGS told DeSmog UK that it only played “an observatory role” regarding the monitoring of seismic events near fracking sites.

“We record what we observe,” she said. “Operators [fracking companies] have their own monitoring process in place.”

A spokesman for the Department of Business, Energy and Industrial Strategy (BEIS) said that OGA was responsible for running and overseeing the traffic light system.  

Lowering of seismic standards

The current traffic light system, which was introduced in 2014 to regulate fracking companies’ activities during seismic events, includes a caveat.

In its fracking guidelines, the OGA states that the 0.5ML threshold above which companies have to suspend hydraulic fracturing “may be adjusted upward if actual experience shows this can be done without compromising the effectiveness of the controls”.

Speaking to The Times, Francis Egan, Cuadrilla’s chief executive, said the threshold for a red light that requires fracking to stop should be raised from 0.5ML to 2ML.

Egan said the 2ML benchmark was appropriate because according to the British Geological Survey tremors of that magnitude were not usually felt by people and that anything below 2ML was considered microseismicity.

He said this would “provide more than adequate assurance that no harm or damage could arise from fracking” and compared the UK’s traffic light system with the US system where a red light is given between 2.7ML and 4.5ML depending on the state.

Egan added that the UK’s current traffic light system was allowing every tremor above 0.5ML to be “treated as major news” and was “heightening public concern”.

Earlier this month, Greenpeace’s investigative unit Unearthed revealed that energy minister Claire Perry suggested that the government could weaken seismic activity standards at fracking sites.

Unearthed obtained a letter sent to Kevin Hollinrake, Conservative MP for Thirsk and Malton, in which Claire Perry said the traffic lights system is “set at an explicitly cautious level but, as we gain experience in applying these measures, the trigger levels can be adjusted upwards without compromising the effectiveness of the controls”.

Following criticism from anti-fracking campaigners, the government said that it had “no plans to make changes” to the traffic light system for now.

Image Credit: Horia Varlan/Flickr/CC BY 2.0