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At the beginning of April, the booming of the pandemic coronavirus in Europe, the seismologist at the Royal Observatory of Belgium Thomas Lecoq, published in Nature a study which reported that cessation of human activities was having an unexpected consequence: the reduction of the vibrations of the Earth.

Now, Lecoq and his team have led, along with the five international scientific institutions, including the Consejo Superior de Investigaciones Científicas (CSIC), a more comprehensive investigation, which confirms that the different measures taken to stop the spread of the pandemic have given rise to the “seismic silence” longer and more pronounced of the entire recorded history of the Earth. The new study was just published in Science.

The research confirmed what Lecoq already anticipated in April, and the pictures of thousands of cities deserted were assumed: the “seismic noise” caused by human activities was more pronounced in the most densely populated areas. This unusual quiet, in addition, allowed seismologists all over the planet to capture the signs of an earthquake more weak , normally hidden by the movement of humans, which will help us to differentiate with more accuracy than ever before-the seismic noise of natural caused by our daily activities.

“we Know that human activity causes vibrations that spread through the soil,” explains Jordi Díaz, CSIC researcher at the Institute of Geosciences of Barcelona-, and that the source of the vibrations with frequencies between 1 and 15-20 Hz recorded by the seismometers of a more or less continuous is related to the traffic, trains or industrial activity, among others. Therefore, in this study we have collected a large amount of seismic data from nearly 300 recording stations distributed throughout the planet, and we have analyzed the variations of energy in that frequency band from four months before the start of the confinement to the present”.

The so-called seismic noise is caused by vibrations that travel through the interior of the Earth in the form of waves. These waves can be caused by earthquakes, volcanoes, bombs… but also by traffic, factories and other forms in which is manifested the constant and continuous human activity.

unprecedented in the history

The fall of the seismic noise caused by human in 2020 is something that has no precedent. The greatest reduction, as is logical, is produced in urban areas, but the study also found subtle changes in the sensors buried hundreds of meters below the earth and in the most remote areas, and depopulated the planet.

Typically, the noise due to anthropogenic (caused by man) it dampens during the quiet periods of the year, such as the Christmas holidays or the chinese new Year , as well as during the evenings of each weekend. However, the observed fall during the confinement has been overshadowed by completely any previous registration.

To gather data, the scientists analyzed the measurements from a global network of 268 seismic stations of 117 countries, and found significant reductions of noise with respect to the normal in periods of low activity in 185 of these stations. Starting with China at the end of January and following by Europe and the rest of the world in march and April, the researchers were following the “wave” of calm until may, to the extent that different regions of the globe were taking measures to tackle the pandemic.

The greatest reductions were found in cities such as Singapore or New York , but were also observed drops in seismic noise in the remote areas like the Black Forest of Germany or of Rundu, in Namibia . The seismometers private, which tend to measure the noise at points more concrete, they noticed large falls around the colleges and universities, sometimes up to 20% greater than those seen during the school holidays. In countries such as Barbados, where the lock coincided with the tourist season, the seismic noise decreased by up to 50%.

The noise does not cease

During the last few decades, the seismic noise has been increasing in all over the world at the same rate in growing populations and economic activities. Therefore, the confinement and the cessation of most of the activities have provided a unique opportunity to study its environmental impacts, among them the reduction of emissions and pollution levels of the atmosphere. But that stop global also has given seismologists an unprecedented opportunity to hear the natural vibrations of the Earth without the distortions of the contribution human.

The study, for example, explains that during the period of calm has been possible to listen to the first and still weak signs of an earthquake in the making, previously hidden by the incessant background noise. Learn to distinguish between the two could mean that in the future we will be able to warn with a lot more precision about the imminence of a natural disaster.

The own Lecoq says, “with increasing urbanization and the growth of populations around the world, more and more people will live in areas geologically hazardous. Therefore, it is more important than ever to be able to distinguish between the seismic noise of natural and human-caused. This research could help to put in place a whole new field of study”.