The governments of different countries are trying to restrain the spread of the SARS-CoV-2 coronavirus by introducing bans on free movement and restricting the work of public institutions and places. Such measures lead to a sharp reduction in economic activity, construction and traffic flows. They are recorded even by sensitive seismometers – tools with which geologists monitor the fluctuations of the earth’s crust.
Seismologists from Brussels were the first to notice this. A post on the Belgian Royal Observatory’s blog on Twitter noted that employees switched to remote mode, while their tools show a marked reduction in fluctuations due to a drop in human activity.
Our staff is teleworking. The earth continues shaking. Ground movements at frequencies 1-20 Hz, mainly due to human activity (cars, trains, industries,…) are much lower since the implementation of the containment measures by the government. #StayHome @ibzbe @CrisiscenterBE pic.twitter.com/pGgQAyLuUP
— Seismologie.be (@Seismologie_be) March 20, 2020
According to an employee of the observatory, Thomas Lecocq, the sensors were originally located in the suburbs of Brussels, but over the past decades they have been surrounded by a bustling urban environment and are constantly recording its “seismic background”. “If the snow has passed, then everything is quiet”, the geologist says, “and if the marathon passes, then we can notice that people ran”. Nevertheless, now even at the height of the working week, the level of background fluctuations in Brussels is comparable to a calm snowy weekend.
The baton of the Belgians was picked up by seismologists from other countries: scientists from France, New Zealand, and Great Britain reported a similar drop in noise. By themselves, this data is not a big surprise. However, scientists plan to take advantage of the sudden lull time. The fact is that understanding the nature of the noise that is introduced into the work of seismographs by human activity will make it possible to better isolate the desired signal from the collected data.
In addition, such high-frequency oscillations are created by many natural processes, including wind and ocean waves. In densely populated areas, they are practically suppressed by the noise of human activity, but now they are more visible. This rare moment should be used in order to better find out their properties and learn how to use them to get more information about what is happening under the surface of the Earth.