Why is it trembling so much in Mexico? 6 facts (2018) 1:13
(.) – The streets of the cities, once crowded, are now empty. Traffic on the roads has been minimized. And less and less people can be found walking outside their houses.
Global containment measures to combat the spread of the coronavirus have apparently made the world much calmer. Scientists are also noticing.
Throughout the world, seismologists are observing far less environmental seismic noise – that is, the vibrations generated by cars, trains, buses, and people who carry out their daily lives. And in the absence of that noise, Earth’s upper crust moves a little less.
Thomas Lecocq, geologist and seismologist at the Royal Observatory of Belgium, first noted this phenomenon in Brussels.
Brussels is seeing a 30% to 50% reduction in environmental seismic noise since mid-March, when the country began implementing school and business closings and other social distancing measures, according to Lecocq. That noise level is on par with what seismologists would see at Christmas, he said.
Less noise means seismologists can detect smaller events
The reduction in noise has had a particularly interesting effect in Brussels: Lecocq and other seismologists can detect smaller telluric movements and other seismic events that certain seismic stations would not have recorded.
Take, for example, the seismic station in Brussels. In normal times, according to Lecocq, it is “basically useless.”
Seismic stations are generally installed outside of urban areas, because reduced human noise makes it easier to detect subtle vibrations in the ground. The one in Brussels, however, was built over a century ago and since then the city has expanded around it.
The daily buzz of city life means that the station in Brussels does not usually detect smaller seismic events. Seismologists would instead rely on a separate drilling station, which uses a pipeline in the ground to monitor seismic activity.
“But at the moment, due to the tranquility of the city, it is almost as good as the deep one,” said Lecocq.
Seismologists in other cities are seeing similar effects in their own cities.
Paula Koelemeijer posted a graph on Twitter showing how noise has been affected in West London, with declines in the post-school and social gathering places in the UK and again after a closure was announced of the government.
Celeste Labedz, a doctoral student at the California Institute of Technology, released a chart showing a particularly sharp drop in Los Angeles.
Still, seismologists say the noise reduction is a sobering reminder of a virus that has sickened more than a million people, killed tens of thousands, and stopped the normal rhythms of life.
People are paying attention to the confinement rules
Lecocq said the charts showing human noise are evidence that people are listening to authorities’ confinement orders and to minimize external activity as much as possible.
“From a seismological point of view, we can motivate people to say, ‘Look. They feel that they are alone at home, but we can tell them that everyone is at home. They are all doing the same. Everyone is abiding by the rules, ‘”he said.
The data can also be used to identify where containment measures might not be as effective, said Raphael De Plaen, a postdoctoral researcher at the National Autonomous University of Mexico.
“That could be used in the future by decision makers to say, ‘OK, we are not doing things right. We need to work on that and make sure that people respect it because this interests us all. ‘