The effect of 2020 COVID-19 lockdown measures on seismic noise recorded in Romania

Abstract

Abstract. After the World Health Organization declared COVID-19 a pandemic in March 2020, Romania followed the example of many other countries and imposed a series of restrictive measures, including restricting people's mobility and closing social, cultural, and industrial activities to prevent the spread of the disease. In this study, we analyze continuous vertical component recordings from the stations of the Romanian Seismic Network – one of the largest networks in Europe, consisting of 148 stations – to explore the seismic noise variation associated with the reduced human mobility and activity due to the Romanian measures against COVID-19 in detail. We focused our investigation on four frequency bands – 2–8, 4–14, 15–25 and 25–40 Hz – and found that the largest reductions in seismic noise associated with the lockdown correspond to the high-frequency range of 15–40 Hz. We found that all the stations with large reductions in seismic noise (>∼ 40 %) are located inside and near schools or in buildings, indicating that at these frequencies the drop is related to the drastic reduction of human activity in these edifices. In the lower-frequency range (2–8 and 4–14 Hz) the variability of the noise reduction among the stations is lower than in the high-frequency range, corresponding to about 35 % on average. This drop is due to reduced traffic during the lockdown, as most of the stations showing such changes in seismic noise in these bands are located within cities and near main or side streets. In addition to the noise reduction observed at stations located in populated areas, we also found seismic noise lockdown-related changes at several stations located far from urban areas, with movement of people in the vicinity of the station explaining the noise reductions.

Variabilities in Urban Ambient Noise Before, During, and After Covid-19 Lockdown in the Peruvian Capital

“…A similar approach to highlighting the noise change at a particular frequency range can be seen in other related studies (e.g., Pandey et al, 2020;Poli et al, 2020;Somala, 2020;Yabe et al, 2020;Arroyo-Solórzano et al, 2021;Grecu et al, 2021;Kuponiyi and Kao, 2021;Nimiya et al, 2021;Pérez-Campos et al, 2021;Shen and Zhu, 2021). This is the frequency range where most of the day-to-day human activities occur like walking, traveling and other related cultural activities.…”

Seismic Background Noise Levels in Italian Strong Motion Network

“…Previous studies showed that during the COVID-19 lockdown there was decrease in noise levels due to the reduction of humanrelated activities, and as recorded by both broadband (Poli et al, 2020;Xiao et al, 2020;Lecocq et al, 2020;Somala, 2020;Dias et al, 2020;Roy et al, 2021;Grecu et al, 2021;Cannata et al, 2021) and strong motion (Yabe et al, 2020;Łukasz Ścisło et al, 2021) stations. These activities were affecting our stations more significantly since several of the RAN stations are located inside or near to the public buildings.…”

Achievements and Prospects of Global Broadband Seismographic Networks After 30 Years of Continuous Geophysical Observations

“…Global government-imposed lockdowns to combat the COVID-19 pandemic have intensified the study of anthropogenic seismic noise, as the staggered easing of restrictions would aid the characterization of dominant noise sources. At the same time, the reduced noise levels during lockdowns make it possible to detect natural events that otherwise drown in the noise (De Plaen et al, 2021;Grecu et al, 2021) and thus improve seismic hazard estimates. Notably, in a global study of lockdown effects on seismic amplitudes, Lecocq, Hicks, et al (2020) also observed a significant reduction in seismic noise at 20 GSN stations.…”