When it comes to earthquakes, countries such as Japan, Indonesia and Mexico often suffer.
But Surrey residents were left stunned after their homes were hit by a series of more than 100 small earthquakes in 2018 and 2019.
The earthquakes occurred in Newdigate and surrounding areas and reached magnitudes of 1.34 to 3.18.
Several homes experienced tremors, while others saw cracks begin to appear in the walls and ceilings.
Since the mysterious earthquakes occurred, geologists have been divided over the likely cause.
While some experts suggested that oil extraction at the Horse Hill well in Horley could have been the cause, others argued that this location was too remote to have caused the Newdigate earthquakes.
Now UCL scientists have solved the mystery – and say this oil extraction was in fact the likely culprit.
“Our findings indicate that oil extraction is likely to have caused the earthquakes,” said Dr. Matthew Fox, lead author of the study.
Residents in Surrey were left stunned after their homes were hit by a series of more than 100 small earthquakes in 2018 and 2019
The earthquakes occurred in Newdigate and surrounding areas and reached a magnitude of 1.34 to 3.18
The ‘swarm’ of tremors hit Newdigate from April 2018 to early 2019, prompting dozens of reports to the British Geological Survey (BGS).
Residents told BGS that their “furniture was shaking very gently” and that “everything was moving forward and then backward.”
Others described “a loud bang and a strong crash and jolt as if something had fallen on the house” and “a general rumbling that lasted for a few seconds.”
Some geologists were quick to blame the earthquakes on the Horse Hill well in Horley, a controversial oil drilling site about five to 10 kilometers away.
However, others argued that the pattern of earthquakes did not correspond to oil extraction.
To get to the bottom of this, the UCL researchers ran more than a million simulations, estimating the frequency of earthquakes based on the timing and volume of oil extraction.
Their results showed that the predictions roughly matched what happened.
According to experts, this indicates a link between oil extraction and earthquakes.
The story was further complicated by the fact that seismometers were not installed in Newdigate until after the first, larger earthquakes had occurred.
Some geologists were quick to blame the Horse Hill well in Horley – a controversial oil drilling site about five to 10 kilometers from Newdigate.
“Our study suggests there is a link between the earthquakes and oil extraction at Horse Hill, but we cannot rule out that this link is coincidental,” Dr Fox said.
“More work needs to be done to understand whether this is cause and effect.”
Extracting oil changes the fluid pressure in the rock from which the oil is extracted, the researchers explain.
While it may sound small, this pressure change could potentially spread through tens of kilometers underground to intersect a fault.
Because faults are often under significant pressure, even a small change in stress can cause the rapid movement of rock, leading to an earthquake.
The story was further complicated by the fact that seismometers were not installed in Newdigate until after the first, larger earthquakes had occurred.
This means that any smaller earthquakes that might have occurred before were not recorded.
“Our research highlights the importance of monitoring the seismicity of areas where oil extraction could take place before any work begins,” said Professor Philip Meredith, co-author of the study.
The British Geological Survey has collected all the earthquakes felt in Britain since the year 1382. Pictured: Top ten largest earthquakes in Britain
‘Caution should be the magic word. There’s no point in saying you don’t have a problem when you might.
‘There has been no significant seismic activity in Surrey for decades, so these earthquakes were unusual events.
“However, unusual events happen in nature, so we cannot rule out that the timing of the oil extraction was a coincidence.”
Surrey residents can rest easy for now as Horse Hill halted production in October after its planning permission was quashed in a landmark court case.
High Court judges ruled that the full climate impact of the project should have been considered before it was approved by Surrey County Council.
However, people in nearby West Sussex could soon face their own earthquakes as another project has received council approval to carry out exploratory oil drilling in Balcombe.
This is subject to a legal challenge by a residents’ group, and the case is expected to be heard by the Court of Appeal this month.