New Delhi (NVI): As much of the world has been grounded to a halt in 2020 due to the spread of the novel coronavirus, researchers from Imperial College London have delved into what these lockdowns have meant for human-caused Earth vibrations, leading to the discovery of what they say is the longest and most pronounced quiet period of seismic noise in recorded history.
Seismic activity doesn’t just come from earthquakes, volcanoes and landslides. Everyday human activity also gives rise to vibrations that travel through the ground as seismic waves, something we call “anthropogenic noise”.
The new study, published in Science, centers on seismic noise generated by vibrations in the Earth. While these can come from natural phenomena like earthquakes and volcanoes, they can also be generated by human activity such as travel and industry.
It was found that seismic noise dropped by an average of 50 percent in 77 countries between March and May 2020. The seismic lockdown effect was even observed in remote areas and in boreholes several hundred metres below the ground.
These vibrations are measured by seismometers, and by looking at data taken from stations around the world scientists can track declines in human-generated seismic noise.
The largest drop in anthropogenic noise was seen in dense urban areas such as New York City and Singapore. But the reduction was also observed in quieter locations such as Germany’s Black Forest and the small city of Rundu in Namibia.
There was a strong match between how much seismic noise fell in a particular area and the change in the amount of human movement recorded there, as measured using mobile phone data made publicly available by Google and Apple.
This correlation means open seismic data can act as a broad proxy for tracking human activity almost as it happens – as people reduce their movements, seismic noise quickly decreases.
-CHK
