A group of scientists reveals a 50% reduction in seismic noise generated by human activity.

Different countries have established measures to confine their population due to COVID-19.

The pandemic COVID-19 has caused a global stoppage of human activity. Citizens of different countries have been confined to their homes for weeks, ceasing to use transport during that period and causing the closure of some companies and factories.

An international study, with the participation of the Higher Council for Scientific Research (CSIC), has monitored this activity during the first months of 2020 through seismometers, devices that are usually used to capture the vibration of the ground after earthquakes.

The data, which is published in the journal Science, reveal that during the period of lockdown global anthropogenic seismic noise has decreased by 50%, making it the quietest since records are available.

“We know that human activity causes vibrations that propagate through the ground and that the origin of vibrations with frequencies between 1 and 15-20 Hz that are recorded by seismometers more or less continuously is related to the traffic, the trains or industrial activity, among others ”, he explains Jordi Díaz, CSIC researcher at the Barcelona Geosciences institute.

Therefore, in this study, scientists have collected a large amount of seismic data from more than 300 stations registry distributed all over the planet. “We have analyzed the energy variations in this frequency band from four months before the start of confinement to the present,” continues Díaz.

The data has confirmed what was seen on the streets of large cities. Seismic noise caused by human activity was cut in half during the first months of the year as a result of a drastic drop in human activity since the beginning of February in places like Beijing (China) or Hong Kong and since mid-March in the rest of the world.

“It can be seen that there has been a progressive recovery of the noise level in recent months, but the levels prior to confinement have not yet been reached,” says the CSIC scientist.

A worldwide measurement

In order to have a vision on a planetary scale, the researcher Thomas Lecocq, of the Royal Observatory of Belgium and leader of the work, developed an analysis system to unify the criteria for studying the data by the international seismological community.

Thus began a collaboration in which 76 authors from 66 institutions in 27 countries have worked in a coordinated manner. The CSIC has participated with the analysis of data recorded in the seismic station installed in Geosciences Barcelona, ​​in the university area of ​​the city, and the 15 stations distributed by schools in Barcelona within the framework of the SANIMS citizen science project.

“The decrease in human-produced vibrations has made it possible to identify signs of small earthquakes that would have gone unnoticed. Furthermore, this work shows that seismometers can be a good tool for monitoring non-geological processes. Since their installation and maintenance is easy and their cost is not excessive, they can be a good option to study multiple processes, both of human origin and of natural origin ”, concludes the scientist.