Earthquakes that prompted Surrey and Sussex to mass protests were not caused by fracking, a new report suggests.
Scientists have found no evidence that fracking is responsible for the series of recent quakes near Gatwick Airport, known as the & # 39; Surrey Swarm & # 39 ;.
The 34 earthquake series, with a magnitude of up to 3.2 on the Richter scale, shook homes and panicked residents within a few miles of two active oil extraction sites in Brockham and Horse Hill in Surrey.
Green campaigners asked for a ban on fracking during the swarm that took place between April 2018 and May of this year.
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Earthquakes that prompted Surrey and Sussex to mass protests were not caused by fracking, a new report suggests. Pictured: Stephen Hicks and Dr. David Hawthorn installed a seismometer near one of the affected areas
The British Isles do not lie along a tectonic plate boundary and earthquakes are rare, which causes concern that the shocks were caused by nearby drilling and extraction.
But scientists at Imperial College London believe that natural causes were behind the earthquakes and said their proximity to fracking sites & # 39; probably coincidence & # 39; used to be.
The first in-depth study of the earthquakes did not find a direct link between oil extraction and earthquakes in the region.
Study leader Dr. Stephen Hicks, from the Imperial Earth Sciences and Engineering Department, said: “The earthquakes seem to have occurred naturally and our findings suggest that their proximity to oil extraction sites is probably a coincidence.
& # 39; This is not the first time that earthquakes seem to come out of nowhere and without human input.
& # 39; The swarm, like most natural earthquakes in the UK, may have been caused by continuous collision of the African and Eurasian tectonic plates in the Mediterranean Sea – the nearest plate boundary of the UK – that emphasizes the crust and causes earthquakes throughout Europe. & # 39;
Scientists have found no evidence that fracking is responsible for the series of recent quakes near Gatwick Airport, known as the & # 39; Surrey Swarm & # 39 ;. Pictured: a map with earthquake data in England and Wales, with the study area south of London
Pictured: a 2D-generated computer-generated image of the subsurface below the earthquake zone with the locations of earthquakes and old geological faults. Green vertical lines show error lines
The imperial team followed the timing, strength and distribution of the earthquakes by using seismometers to measure vibrations in the ground.
They also mapped the distances between the quakes and the extraction sites and investigated the depth at which they took place.
Their results showed that the quakes were divided into a tight cluster more than 3 km away from the extraction sites that researchers said they were too far away to link to fracking.
Dr. Hicks said: & # 39; It would be unprecedented for this type and scale of oil extraction to hit locations more than a kilometer away. & # 39;
Researchers discovered that the Surrey Swarm earthquakes moved old errors horizontally, indicating that the earthquakes would probably have happened, regardless of the oil extraction in the area.
Most natural earthquakes in the UK cause rocks on either side of weak spots in the ground, known as errors, to move horizontally.
Earthquakes caused by oil extraction, on the other hand, cause stones to move vertically on either side of faults.
Dr. Hicks said: & # 39; The ground vibrations of earthquakes provide clues that indicate their cause.
& # 39; There are more and more examples of human activity causing earthquakes worldwide, but it can be difficult to figure out which newer cases are natural and which are caused by people. & # 39;
Researchers also used earthquake data from existing sensors in civilian homes – known as & # 39; Raspberry Shakes & # 39; – who have been listening to seismic activity in the area since the end of 2017.
Based on data from the seismometers, the research team investigated and compared various characteristics of the Surrey earthquakes with previous earthquakes caused by human activities as well as natural causes in the UK and elsewhere.
Dr. Hicks added: & Tens of years of instrumental recordings and hundreds of years of historical earthquake reports show that similar seismic swarms have occurred earlier in the UK due to long-term tectonic stress and without a clear link to human activities. & # 39 ;
To measure the depth at which the earthquakes occurred, scientists compared the location of the earthquakes with images of underlying rock layers.
The images were made by measuring the reflection of sound waves from each layer.
They discovered that although the earthquakes in Surrey were shallow (about 2.5 km deep), they occurred deeper than rock formations from which oil is extracted (less than 1 km deep).
The full findings of the study were published in the journal Seismological survey letters.
HOW DOES FRACKING TRIGGER EARTHQUAKES WORK?
Earthquakes are usually caused when underground rock suddenly breaks past an error.
This sudden release of energy causes the seismic waves that make the ground vibrate, and in extreme cases the Earth's crust can even be split to the surface.
Fracking works by injecting huge amounts of water into the rocks around a natural gas deposit or hydrothermal well.
The water breaks the rocks, causing dozens of cracks through which gas and heat can escape to the surface.
Fracking causes earthquakes by introducing water into fault lines, lubricating the rocks and making them more likely to slip.
When two blocks of rock or two plates rub against each other, they catch each other.
The rocks are still pushing against each other, but not moving, construction pressure that is only released when the rocks break.
During the earthquake and beyond, the slabs or blocks of stone begin to move and keep moving until they get stuck again.
There are questions about whether a magnitude of 5.6 that hit Oklahoma – the largest earthquake ever recorded in the state – was caused by the controversial process.
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