On 1 April 2018, an earthquake struck near Newdigate in Surrey. It was followed by further quakes over the next two months, in a swarm that is unprecedented in the last half century. There have so far been 172 recorded tremors (at the time of writing) and they continue to occur.

Seismologists plotted the epicentres between Newdigate and Charlwood, just 3km from the Horse Hill drill site and 8km from Brockham.

The earthquakes have caused injury and damage to property, as well as considerable anxiety to residents across a wide area. Some have been felt over 10km away. Residents report loud bangs and shaking, with many thinking a plane or lorry had crashed nearby. As the quakes are at shallow depth, the intensity of the shaking at the surface is higher than would be felt from deeper earthquakes of a similar magnitude.  The strongest earthquake so far was given an intensity of 5 and 1,600 people reported feeling it to the British Geological Survey.

Cause of the quakes

In October 2018, the Oil & Gas Authority (OGA) hosted a workshop to look into the cause of the quakes, which was attended by academics and regulators and chaired by the British Geological Survey. The report of the workshop concluded that there was no causal link between the seismic events and oil and gas activity. However this did not represent a consensus and some geologists took the opposite view.

The workshop disregarded the existence of Horse Hill, as they maintained that no work was being carried out there at the time of the first quakes. This has later been proven to be false. It only considered drilling at Brockham, and decided that was not the cause.

Specialists in Structural and Petroleum Geology at the Edinburgh University School of GeoSciences, who have expertise in seismic surveying of the deep underground and pressure effects on stress transfer, as well as practical experience of boreholes, believe that activities at Horse Hill were causing the quakes. They examined the evidence and wrote a briefing, ‘Further Potential for Earthquakes from Oil Exploration in the Weald‘, published in February 2019, said: “Our assessment supports the concern that Horse Hill oil exploration triggered the earthquakes. We infer that future oil exploration and production close to critically stressed faults in the Weald is likely to result in similar earthquake events.”

Conflict of interest

This highlights the contradiction at the heart of oil and gas regulation. The primary aim of the Oil and Gas Authority is to maximise oil and gas production across the country – which conflicts with its responsibility as a regulator.

Call for a moratorium

The Weald Action Group has called for a moratorium on all oil and gas drilling in the Horse Hill area until there is a thorough understanding of the seismic risks and consensus on safety. The case for employing the precautionary principle is obvious.

Even small earthquakes can cause considerable damage over time. Groningen in the Netherlands is one example of earthquakes caused by gas extraction. After years of small earthquakes, houses began to collapse and over a billion Euros has so far been paid out in compensation. Complaints from local residents were ignored for years and the operating company denied responsibility – just as is happening in Surrey.

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