COVID-19 lockdown effects on the seismic recordings in Central America

Mario Arroyo-Solórzano,Frédérick Massin,Lepolt Linkimer,Diego Castro-Rojas,Ivonne Arroyo,Robin Yani

doi:10.5194/se-12-2127-2021

Mario Arroyo-Solórzano, Frédérick Massin + Show 4 more

Open Access

https://doi.org/10.5194/se-12-2127-2021

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Abstract

Abstract. A noticeable decrease in seismic noise was registered worldwide during the lockdown measures implemented in 2020 to prevent the spread of COVID-19. In Central America, strong lockdown measures started during March of 2020. In this study, we used seismic stations from Costa Rica, Guatemala, El Salvador, and Nicaragua to study the effects of these measures on seismic records by characterizing temporal variations in the high-frequency band (4–14 Hz) via spectral and amplitude analyses. In addition, we studied the link between the reduction in seismic noise and the number of earthquake detections and felt reports in Costa Rica and Guatemala. We found that seismic stations near the capitals of Costa Rica, Guatemala, and El Salvador presented a decrease in their typical seismic noise levels, from 200 to 140, from 100 to 80, and from 120 to 80 nm, respectively. Our results showed that the largest reduction of ∼ 50 % in seismic noise was observed at seismic stations near main airports, busy roads, and densely populated cities. In Nicaragua, the seismic noise levels remained constant (∼ 40 nm), as no lockdown measures were applied. We suggest that the decrease in seismic noise levels may have increased earthquake detections and the number of felt reports of low-magnitude earthquakes. However, the variations observed in several seismic parameters before and after the lockdown are not significant enough to easily link our observations or separate them from other contributing factors. Our results imply that the study of seismic noise levels can be useful to verify compliance with lockdown measures and to explore their effects on earthquake detection and felt reports.

Highlights

The seismic noise recorded by seismometers includes microseisms and atmospheric, anthropogenic, or cultural noise (Nimiya et al, 2020)
No curfew was imposed on citizens in Costa Rica, a strict vehicle mobility restriction has been maintained throughout the pandemic
For Guatemala and El Salvador, the lockdown measures were very similar to those implemented in Costa Rica; in some cases, the former included restrictions on the mobility of citizens and curfews

Summary

Introduction

The seismic noise recorded by seismometers includes microseisms and atmospheric, anthropogenic, or cultural noise (Nimiya et al, 2020). A reduction in the seismic noise worldwide has been observed coinciding with the lockdown measures to prevent the spread of COVID-19, which was declared a pandemic by the World Health Organization in March 2020 (Sohrabi et al, 2020). This effect was first described for Shillong (India) by Somala (2020), for northern Italy by Poli et al (2020), and at a global scale by Lecocq et al (2020a). Governments have tried to prevent or delay the spread of COVID-19 by enforcing social distancing via measures such as limiting nonessential activities, closing schools and universities, restricting the mobility of the citizens, and shutting down workplaces (Piccinini et al, 2020)

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