The Seismic Sound of Silence in Level 4 Locked-down Aotearoa

The COVID-19 pandemic is paralyzing our ways of life, as we are hunkered down in a Level 4 lock-down. Businesses are closed, and work is moved to home, where possible. Schools are closed, and we live in our “bubbles.” Many of the seismic stations in the Ru network of school seismometers continue to operate, however, and we wanted to share with you some interesting observations. Here is a figure from our station at St. Mary’s Catholic Primary School in Rotorua:

The horizontal scale starts on January 1st of this year, and ends today, April 9th. The vertical scale is the average noise level at the station. There is a lot to see in here. First, the smallest consistent variations are between the days and the nights; Rotorua and St. Mary’s Primary School are much quieter during the nights than during the days. The next scale up, you can see that every 7 days, there is a period of low noise. These are the weekends, which are generally quieter than the weekdays. At an even larger time scale, we see that St. Mary’s  station was less noisy during the Summer Holiday than during term 1 of school. Until two weeks ago, when school closed again, and noise levels dropped to its lowest levels.

This shows that seismometers are sensitive to the noise we humans make, even the not fully grown ones. In this case, the exceptionally low noise levels during the lock-down, lower than the Summer Holiday levels, indicate that station SMC2 is (normally) sensitive to human noise beyond the classroom, such as cars driving in the street. If you don’t believe us, please read the GEONET news, where it is reported that the lock-down in Auckland can be sensed all the way in a borehole 300 m under ground!


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