The latest – and biggest – in a series of earthquakes to hit Surrey this year is “unlikely” to be linked to any activity related to oil or gas exploration, according to the British Geological Survey.
The magnitude 3.0 earthquake, which was widely felt across the Dorking , Reigate and Redhill area, happened on Thursday morning (July 5) at 10.53am. People reported feeling loud bangs, rumbles and buildings shaking.
There have now been seven tremors recorded since April 1 – the first ever recorded in Surrey. They have all been centred close to Newdigate, leading inevitably to questions about why the area is currently experiencing the sudden seismic activity, and whether or not it will continue.
The Horse Hill oil exploration site is close to the epicentre but while drilling and new flow testing of the oil there is planned, it has not yet taken place, and the company behind it has said none of the previous activity there has been associated with any seismic movement.
The BGS, the UK’s national earthquake monitoring agency, said in a statement: “We are unable to say categorically if these earthquakes are related to hydrocarbon exploration or production in the Weald, mainly because of the uncertainties in our estimates of the earthquake epicentres and depths.
“We use a process a bit like triangulation to locate earthquakes and our closest monitoring station was over 50km away, so the errors in our location estimates are several kilometres. Our calculated epicentres for the earthquakes are approximately 4.5km from the Horse Hill well, which is within our calculated uncertainty.”
(Image: Grant Melton)
The statement added: “While it is well known that hydrocarbon exploration and production can result in man-made or ‘induced’ earthquakes, such events usually result from either long-term hydrocarbon extraction, or the injection of fluids (e.g. hydraulic fracturing) during production. It seems unlikely that flow testing, even if it had taken place, would result in induced seismicity.
“Although there have been no other instrumentally recorded events in the region in the last 50 years (and none at all in Surrey since records began), there is evidence for historical earthquakes in the last 500 years, therefore a natural origin for these earthquakes can’t be ruled out at this stage.”
On Thursday, Green Party MEP for the south east Keith Taylor said that the seismic activity in an area where unconventional fossil fuel drilling and testing is active is “clearly extremely concerning”, and called for any oil and gas activity in the region to be halted.
At Horse Hill, near Hookwood , a borehole was drilled in 2014 and flow testing was carried out in 2016.
Horse Hill Developments was granted permission for the drilling of a second borehole in November and the Environment Agency has granted a permit for extended flow testing.
Stephen Sanderson, executive Chairman of UK Oil and Gas (UKOG) , which is behind the Horse Hill operation, said: “There has been no subsurface activity at Horse Hill since March 2016.
“We are currently preparing to conduct a flow test using a crane. No flow has yet taken place. We are not drilling and operations utilise a crane, not a drill rig. We should stress that the work we are planning has the same seismic impact as any type of construction work requiring the use of such a crane.
(Image: Grant Melton)
“We would also like to point out that there was no recorded seismicity associated with our 2014 drilling and 2016 flow testing, nor are we aware that any of the other 80-plus wells drilled or flowed in the Weald are associated with any seismicity. Furthermore, as the BGS have stated, the source of this seismicity is related to a deep-seated basement fault at around 5.5 km below surface, 4.5 km deeper than our activities at Horse Hill.”
Elsewhere in Surrey, oil sites have been the focus of protests. At Leith Hill, Europa Oil and Gas is awaiting a decision by the Environment Agency on whether or not it will be permitted to carry out exploratory drilling .
(Image: David Lenigas)
Surrey Live has approached the Environment Agency for comment.
Thursday’s magnitude 3.0 tremor follows six others this year , including one on Friday, June 29.
Other stronger quakes have been felt elsewhere in the UK this year, including one measuring 3.8 in Grimsby on June 9, which was felt across eight counties. A 4.6 magnitude earthquake, felt across Wales and the south west in February, was the largest on the UK mainland in ten years.
Surrey Live is not aware that the recent tremors have caused any damage locally.