Containment results in dramatic reduction in seismic noise

Many scientists are currently seeing a decrease in seismic noise, due to the reduction in human activities since the implementation of restrictive measures to try to stop the spread of the coronavirus. They said it could allow sensors to spot small earthquakes and improve monitoring of volcanic activity.

“Noise reduction of this magnitude is usually only felt briefly around Christmas”

Like avalanches or volcanic eruptions, human activities (transport, travel, industry, etc.) generate seismic waves that pass through the earth’s crust. Although the effects of individual sources may be small, when these are combined, they produce background noise which reduces the ability of seismologists to detect other signals occurring at the same frequency. Recently, data from a seismometerRoyal Observatory of Belgium have shown that the measures taken to halt the spread of Covid-19 at Brussels have reduced the seismic noise of anthropic origin.

The measures included the closure of schools, restaurants and other public places from March 14, as well as the prohibition of non-essential travel from March 18. According to Thomas Lecocq, seismologist atRoyal Observatory of Belgium, ” noise reduction of this magnitude is usually only felt briefly around Christmas

The current decrease has the effect of increasing the sensitivity of the observatory equipment, improving its ability to detect waves in the same high frequency range as noise. Result: the installation’s surface seismometer is now almost as sensitive to light earthquakes as a sensor installed at the bottom of a 100-meter borehole.

This graph shows the evolution of seismic noise in Brussels since the beginning of 2020, characterized by a decrease in seismic noise of human origin in the last two weeks.

More precise seismic measurements

If these restrictions and containment measures continue in the coming months, sensors installed in cities around the world could be more effective in detecting aftershocks, according to Andy Frassetto, seismologist atIncorporated Research Institutions for Seismology of Washington DC. ” You will get a signal with less noise at the top, which will allow you to extract a little more information for this type of event.. “

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The reduction in seismic noise could also benefit scientists who use natural background vibrations, such as those caused by the crushing of underwater ocean waves, to probe the Earth’s crust. Since volcanic activity and variations in groundwater affect the speed at which these natural waves travel, seismologists could study these events by monitoring the time it takes for a wave to reach a given sensor.

Although a similar decrease was also recorded at Los Angeles, not all seismic monitoring stations will see an effect as marked as that of Brussels. A large part of them are in fact located in isolated regions, in order to limit seismic noise of human origin.

– zhu difeng /

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