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Cumbrian coal mine | Geotech experts play down earthquake claims

Geotechnical experts have urged caution over claims from a campaign group that the proposed Cumbrian coal mine could cause earthquakes.

Before the start of the public inquiry into the mine – which began yesterday – campaign group Radiation Free Lakeland said that the development poses induced earthquake and subsidence risk.

The group believes that “mining induced seismicity is likely to occur” at the coal mine, and also emphasised that nuclear waste site Sellafield is 8km away.

“The majority of anthropogenic-related earthquakes were caused by coal mining and the decline in their numbers from the 1980s to the 2000s was concurrent with a decline in UK coal production," Radiation Free Lakeland said.

"The coal mine will induce earthquakes in the vicinity of the world’s riskiest nuclear site – that is a given – let's hope and pray that the massive silence from NGOs over the nuclear elephant in the room does not give the government (who are employing the coal boss) wriggle room to approve the coal mine.

"We urge all those speaking against the mine at the public inquiry to give at least a mention to the fact that this coal mine would mine out voids faster than any previous coal mine in UK history and would induce earthquakes and cause subsidence in the Irish Sea and Sellafield area."

Geotechnical specialist Clive Edmonds said that “in principle, mining can induce low magnitude, shallow depth earthquake activity”.

“Such activity has been noted in many former coal field areas where several different depth coal seams underlying each other were extracted in close proximity to fault lines,” he said.

However Edmonds emphasised that “whether and to what degree” the Cumbrian coal mine will cause earthquake activity “will depend upon the specific mine design and development plan over time taking account of the known regional structural geology”.

Wilgeo director Phil Wilson added that “deep coal mines do cause surface tremors which could erroneously be mistaken for deep seismic events (natural earthquakes)”.

He added: “The critical issue is the magnitude of the coal mining "seismic event " on the Richter scale, which are relatively minor in seismic terms.

“It is perhaps scaremongering to imply that these relatively minor events and surface tremors from coal mining are a hazard to nuclear facilities in Cumbria, which will have already been designed for full seismic loading on the order of 0.2g.”

Overall, University of Leeds engineering geologist Bill Murphy said that while mining-induced earthquakes were common, Radiation Free Lakeland’s claims ignore “important limitations”.

Subsidence, for example, is often associated with mining. However Murphy emphasised that "the deeper the mine, the wider the subsidence bowl but very wide subsidence bowls tend to cause little or no damage because there is no differential movement".

He said: "If you take the subsidence bowl for Boulby mine [in North Yorkshire] for example it is a couple of millimetres deep but spread over a large area. Where subsidence has been a problem elsewhere it is normally crown hole subsidence from poorly capped off mineworkings."

Murphy added that fears raised by Radiation Free Lakeland over liquefaction may also be unfounded as this tends “to be associated with large earthquakes”.

“Liquefaction generally only occurs at M>5.0,” he said. “Mining induced earthquakes tend to be less than 4.0ish."

Plans for the £165M mine were originally approved by Cumbria County Council in October 2020.

Since then communities secretary Robert Jenrick has “called in” the decision and asked the Planning Inspectorate to carry out a formal evaluation of the scheme.

In February, Cumbria County Council said it would reconsider its decision to give the project the go-ahead in order to take into account "new information" in the Climate Change Committee's Sixth Carbon Budget, and in May the council announced that it will remain “neutral with regard to the mine”.