When it comes to earthquakes, countries including Japan, Indonesia, and Mexico tend to bear the brunt.
But residents across Surrey were baffled after their homes were struck by a series of more than 100 small earthquakes in 2018 and 2019.
The earthquakes occurred in Newdigate and the surrounding areas and reached magnitude 1.34 to 3.18.
Several homes experienced shaking, while others saw cracks begin to appear in their walls and ceilings.
Since the mysterious quakes took place, geologists have been divided over the likely cause.
While some experts suggested oil extraction at the Horse Hill well in Horley could be to blame, others argued that this site was too far away to have triggered the earthquakes in Newdigate.
Now, scientists from UCL have solved the mystery – and say that this oil extraction was in fact the likely culprit.
‘Our findings indicate it is plausible that oil extraction triggered the earthquakes,’ said Dr Matthew Fox, lead author of the study.
Residents across Surrey were baffled after their homes were struck by a series of more than 100 small earthquakes in 2018 and 2019
The earthquakes occurred in Newdigate and the surrounding areas and reached magnitude 1.34 to 3.18
The ‘swarm’ of tremors hit Newdigate from April 2018 until early 2019, sparking scores of reports to the British Geological Survey (BGS).
Residents told BGS that their ‘furniture shook very gently’ and ‘everything moved forwards then backwards’.
Others told of ‘a loud bang and strong impact and shake as though something had fallen on the house’ and ‘general rumble that lasted for a couple of seconds’.
Some geologists were quick to blame the Horse Hill well in Horley – a controversial oil drilling site about three to six miles away from the earthquakes.
However, others argued that the pattern of earthquakes did not correspond to oil extraction.
To get to the bottom of it, the UCL researchers ran more than one 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 occurred.
According to the experts, this suggests a link between the extraction of oil and the earthquakes.
The story was complicated further by the fact that seismometers were only installed in Newdigate after the first, larger earthquakes had occurred
Some geologists quickly blamed the Horse Hill well in Horley – a controversial oil drilling site about three to six miles away 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 a coincidence,’ Dr Fox said.
‘More work needs to be done to understand if this is cause and effect.’
Extracting oil changes the fluid pressure in the rock the oil is extracted from, the researchers explain.
While it might sound small, this change in pressure can potentially diffuse through tens of miles underground to intersect a fault.
As faults are often under considerable strain, even a small change in stress can cause the rapid movement of rock – leading to an earthquake.
The story was complicated further by the fact that seismometers were only installed in Newdigate after the first, larger earthquakes had occurred.
This means that any smaller earthquakes that might have occurred before this were not recorded.
‘Our study highlights the importance of monitoring the seismicity of areas where oil extraction might occur before any works start,’ said Professor Philip Meredith, co-author of the study.
The British Geological Survey has collated all the earthquakes felt in Britain since the year 1382. Pictured: Top ten largest UK earthquakes
‘Caution should be the byword. It is no good saying you don’t have a problem when you potentially do.
‘There has been no significant seismic activity in Surrey for decades, so these earthquakes were unusual events.
‘However, unusual events do happen in nature, so we can’t rule out the possibility that the timing associated with the oil extraction was a coincidence.’
Surrey residents can rest easy for now, as Horse Hill suspended production in October, after its planning permission was quashed in a landmark legal case.
Supreme 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 may soon face their own earthquakes, as another project has received council approval to conduct exploratory oil drilling in Balcombe.
This is subject to a legal challenge by a residents’ group, with the case expected to be heard by the Court of Appeal this month.
The Earth is moving under our feet: Tectonic plates move through the mantle and produce Earthquakes as they scrape against each other
Tectonic plates are composed of Earth’s crust and the uppermost portion of the mantle.
Below is the asthenosphere: the warm, viscous conveyor belt of rock on which tectonic plates ride.
The Earth has fifteen tectonic plates (pictured) that together have moulded the shape of the landscape we see around us today
Earthquakes typically occur at the boundaries of tectonic plates, where one plate dips below another, thrusts another upward, or where plate edges scrape alongside each other.
Earthquakes rarely occur in the middle of plates, but they can happen when ancient faults or rifts far below the surface reactivate.
These areas are relatively weak compared to the surrounding plate, and can easily slip and cause an earthquake.
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