The UK findings have come two weeks after seismologists at the Royal Observatory in Belgium observed a 30-50 per cent fall in levels of ambient seismic noise since schools and businesses were closed in mid-March. Seismologists around the world have now begun a collaborative effort to study the fall in seismic noise levels, the BGS press release said.
What is seismic noise?
In geology, seismic noise refers to the relatively persistent vibration of the ground due to a multitude of causes. It is the unwanted component of signals recorded by a seismometer– the scientific instrument that records ground motions, such as those caused by earthquakes, volcanic eruptions, and explosions.
This noise includes vibrations caused due to human activity, such as transport and manufacturing, and makes it difficult for scientists to study seismic data that is more valuable. Apart from geology, seismic noise is also studied in other fields such as oil exploration, hydrology, and earthquake engineering.
Why have seismic noise levels reduced due to coronavirus?
As per the Belgian study, due to the enforcement of lockdown measures around the world to tackle the novel coronavirus pandemic, the Earth’s crust has shown reduced levels of vibration.
According to Dr Brian Baptie, a seismologist at the British Geological Survey, “We measure ground vibrations from earthquakes using seismometers. These are incredibly sensitive so they also pick up other sources of vibration too, including human activity, such as road traffic, machinery and even people walking past. All these things generate vibrations that propagate as seismic waves through the Earth.
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“We compared the average daytime noise levels at seismic stations in the UK in the two week period since the start of the Covid-19 lockdown with the average noise levels for the beginning of the year. The results show reductions in noise levels at most of our stations of between 10-50%.”
How do the reduced noise levels help scientists?
The seismic noise vibrations caused by human activity are of high frequency (between 1-100 Hz), and travel through the Earth’s surface layers. Usually, to measure seismic activity accurately and reduce the effect of seismic noise, geologists place their detectors 100 metres below the Earth’s surface.
However, since the lockdown, researchers have said that they were able to study natural vibrations even from surface readings, owing to lesser seismic noise.
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Due to lower noise levels, scientists are now hoping that they would be able to detect smaller earthquakes and tremors that had slipped past their instruments so far.
According to Dr Baptie, “This might help us detect smaller earthquakes and also see low amplitude parts of the ground motions caused by larger earthquakes.”
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