The pandemic causes the longest period of seismic silence since records are available

The pandemic causes the longest period of seismic silence since records are available

The COVID-19 pandemic has caused a halt in human activity worldwide. Citizens of different countries have been confined to their homes for weeks, stopping the use of transportation 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 soil after earthquakes.

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

The data, published in the journal Science, reveal that global anthropogenic seismic noise has decreased by 50% during the confinement period, 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 registered by seismometers more or less continuously is related to traffic, trains or industrial activity, among others ”, explains Jordi Diaz, researcher at the CSIC at the Barcelona Geosciences Institute.

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

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 consequence of a drastic drop in human activity since the beginning of February in places such as Beijing (China) or Hong Kong and from mid-March in rest of the world.

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

A measurement on a global scale

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

“The decrease in vibrations produced by humans has allowed us to identify signs of small earthquakes that would have gone unnoticed,” says the scientist.

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 registered 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 vibrations produced by humans has allowed us to identify signs of small earthquakes that would have gone unnoticed. Furthermore, this work shows that seismometers can be a good tool to monitor processes not related to geology. Since their installation and maintenance is easy and their cost is not excessive, they can be a good option to study multiple processes, both human and natural origin,” concludes the scientist.

Reference :
Thomas Lecocq, Stephen Hicks, Koen Van Noten, Kasper van Wijk, Paula Koelemeijer, Raphael SM De Plaen, Frédérick Massin, Gregor Hillers, Robert E. Anthony, Maria-Theresia Apoloner, Mario ArroyoSolórzano, Jelle D. Assink, Pinar Büyükakpinar, Andrea Cannata, Flavio Cannavo, Sebastian Carrasco, Corentin Caudron, Esteban J. Chaves, David G. Cornwell, David Craig, Olivier FC den Ouden, Jordi Diaz et al. “Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures”. Science. DOI: 10.1126 / science.abd2438