COVID19 social restrictions having an impact on seismic ambient noise

Miguela Xuereb

The authorities’ pleas for families to stay indoors including Sundays and public holidays to reduce the spread of the COVID-19 virus is being heeded, and confirmation for this comes from an unlikely source – the seismograph stations of the Malta Seismic Network, operated by the Department of Geosciences of the University of Malta.

The network comprises seven state-of-the-art digital seismographs installed over Malta, Gozo and Comino. The primary aim of the Malta Seismic Network is to monitor and evaluate local and regional earthquakes as they happen. But these sensitive instruments also continuously record ground vibrations originating from man-made sources such as traffic and industrial machinery, as well from natural sources such as wind and sea waves.

The figure shows the level of background seismic noise over the past few weeks recorded at the seismic station MSDA installed in the grounds of the University Msida campus. The daily variation in noise level between night and day can be observed and the sharp reductions in daytime noise is evident on Sundays and public holidays.

However, these peaks have dropped even further, by about 20 to 25%,  over the past few weeks, when the public was urged to stay indoors, as shown by the lines on the graph. This indicates a substantial decrease in traffic on the nearby Regional Road and Birkirkara Bypass.

Similar observations have been noted across Europe. Thomas Lecocq, a seismologist at the Royal Observatory in Belgium, discovered that ambient seismic noise has fallen drastically in Brussels since the mid-February, around the time the country closed schools and businesses. Whilst the decrease in social activity is unwelcome by society, it may give seismologists the opportunity to detect smaller earthquakes whose weak signal is usually lost in the cultural noise.

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