With containment, the Earth trembles less

Reading time: 2 min – Spotted on CNN

While half of humanity is now locked up at home, the planet is calmer, and the earth is shaking less.

Since the start of containment measures and the gradual cessation of a certain number of activities, seismologists have observed a strong reduction in ambient seismic noise. This is usually generated by the comings and goings of cars, buses and trains, which cause vibrations, the activity of industries, but also simply by people who go about their daily activities, the cries of children in the schools, etc.

In the absence of these activities, and therefore of this noise, it is the earth’s crust which moves a little less.

Like Christmas

In Brussels, for example, ambient seismic noise has been reduced by 30 to 50% since the announcement of general confinement in Belgium on March 18. According to geologist and seismologist Thomas Lecocq, at the origin of these seismic measurements, this rarely reached noise level is comparable to what can be observed in cities on Christmas Day.

This drop in permanent ground vibrations can allow seismologists to detect earthquakes of small magnitude that seismic stations would not have been able to record in normal times.

The stations are generally located outside urban areas, in order to capture the vibrations of the ground without the measurements being parasitized by human seismic noise. In the Brussels case, however, there is a station in the middle of the city, built in the last century, before the city developed: usually useless for this type of measurement, it is now able to record almost as low vibrations than isolated stations.

With the help of other seismologists, Thomas Lecocq has developed a code on Github to verify how the confinement measures linked to the coronavirus have affected seismic noise around the world.

In Paris, seismologist Claudio Satriano thus took measurements from the Marie Curie seismic station, near the Institut de Physique du Globe de Paris, which showed a marked reduction in noise from March 17 at 11 a.m., when the containment began to take effect.

Same observation in England, in Truro, in Cornwall, where the seismic noise is almost as weak as a Christmas evening:

This reduction in seismic noise linked to human activities does not mean that we should expect a reduction in earthquakes.

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