Scientists have found that the restrictions during a pandemic COVID-19 resulted in a months-long decline in high-frequency anthropogenic seismic noise level to 50 percent. This is the longest and most notable of was periods of attenuation of such noise, according to the researchers, it will help to detect weak signals from underground sources and to assess the overall contribution of the noise of human origin in the seismic data. Article published in the journal Science.
Although seismographs are designed to record and predict earthquakes, these devices record all types of seismic waves — including anthropogenic noise. In the city the noise is most often associated with everyday human activities and therefore provides an almost continuous signal from a series of sources — including transportation and industry. These fluctuations are constantly captured by the seismographs and can prevent the registration of weak tremors, precursors of dangerous geological events.
Therefore, to proactively predict such events, you must learn to distinguish weak signals against the background of anthropogenic noise — and this, in turn, need to understand the nature of the noise. However, this raises a number of challenges — multiple possible sources overlap each other in time and change the position in space of the measuring centres are located non-uniformly, and to monitor public activity for seismological experiments almost impossible. As a result of global and long-term contribution of human activities in the seismic noise remains almost unexplored.
Scientists from 25 countries under the leadership of Thomas Lecocq (Lecocq Thomas) from the Royal Observatory of Belgium has studied the global impact of anthropogenic factors on the seismic noise. For this, the authors analyzed archival data from 337 seismic stations around the world in recent months: from December 2019 to may 2020, while paying attention to the correlation between changes of the noise level and the introduction in the region of the restrictive measures because of a pandemic COVID-19. To highlight the noise caused by human activity, researchers have identified the frequency band signals in the 4-14 Hz, and to improve the quality of the sample stations were selected with long breaks in enrollment or failures in the receivers. In addition, in the course of work were taken into account variations in population density — the scientists compared the data that were collected in the densely populated regions and distant from urban areas.