![]() We remark here that the quantitative correlation between pollutants, vehicular traffic and noise would require a dedicated work also accounting for the changes of meteorological conditions over time. When available, these are also compared with traffic data from local municipalities or other sources and with NO 2 pollutant from local environmental protection agencies. We first show noise amplitude time series, expressed as ground displacement, for some representative sites to focus on how and when noise level changed over time. This choice, discussed in details in “ Methods” section, stems from the need of representing the ambient noise variations with a unit measure readily understandable by a broad scientific community. We will focus on the frequency band for 5 to 20 Hz and retrieve, for each site, a time series of the displacement noise amplitude. The two weeks before the lockdown (Feb 24-March 7, 2020) are used as a baseline (REFWs), while the four subsequent weeks (March 8-April 5, 2020) will be referred as W j, with j = 1,4. 2 and details in the “ Material and methods” section). 1) during 6 weeks across March 10 (timeline in Fig. The seismic dataset for Northern Italy is based on the recordings of 78 seismic stations (Fig. Moreover, with respect to 10, 11, 12, we tackle the causes for the observed spatial and temporal fluctuations in noise reduction with the goal of understanding how they originated. In this work, we focus with higher detail on the regional-scale transition across the March 10 lockdown (DPCM-1), with a combined analysis of time-varying seismic ambient noise and static socio-economic dimensions, such as population density and composition of economic activities (strategic and non-strategic industries). 11 and, at global scale, by Lecocq et al. The general trend of ambient noise reduction after the lockdown has been first described for Shillong (India) 10, for Northern Italy by Poli et al. This effect is modulated at each site according to the ratio between anthropogenic and natural noise and to the source-receiver distance and confirmed by the observed correlation between economic conditions and noise level at global scale 9. Anthropogenic sources are mainly associated with road and rail traffic, cultural and industrial activity causing a characteristic pattern of two superimposed fluctuations with daily and weekly periodicity. the alluvial basin of the Po Plain), ambient noise is high and masks low magnitude seismicity 8. The observation of the anthropogenic noise at high frequency (F > 1 Hz) dates back to the 60′s 7 and, especially in regions with high anthropic activity and poor rock characterization like a large portion of our study area (i.e. This approach is effective in providing insights on the variation of natural and anthropogenic noise sources 4, in seasonality of waves and winds 5, and on the effect of disruptive events like the Super Typhoon Ioke 6. Besides social and economic effects and extensive daily life disruption (any unnecessary individual circulation was prohibited), restrictions also determined a decrease in the seismic ambient noise due to the integrated effects of natural (ocean waves and wind) and anthropogenic sources 1, 2, 3.Īs seismic monitoring networks operate continuously, seismic data can be easily used to track changes in the ambient noise. A second decree, on March 22, extended the closure to all the non-strategic economic activities while few remained fully operative ( hereinafter DPCM-2). The extreme effort of the Italian Government to prevent or delay the diffusion of the COVID-19 resulted in the lockdown of social, cultural, and part of economic and industrial activities over the entire country starting from Ma( hereinafter DPCM-1) imposing social distancing to the entire population. ![]() These results are crucial for the a posteriori interpretation of the pandemic diffusion and the efficacy of differently targeted political actions. A fresh interpretation of seismic noise variations in terms of socio-economic indicators sheds new light on the lockdown efficacy pointing to the causes of such delay: the noise reduction is significant where non strategic activities prevails, while it is small or negligible where dense population and strategic activities are present. The reaction to lockdown was slow and not homogeneous with spots of negligible noise reduction, especially in the first week. Here we show the lockdown effect in Northern Italy, the COVID-19 most affected area, as revealed by noise variation at seismic stations. The Italian Government has decreed a series of progressive restrictions to delay the COVID-19 pandemic diffusion in Italy since March 10, 2020, including limitation in individual mobility and the closure of social, cultural, economic and industrial activities. ![]()
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