On the Effect of COVID-19 Lockdown on Seismic Detection Capability

During 2020, people around the world lived a lockdown of different stages consequence of COVID-19 pandemic, switching almost every daily life activity to a remote version. As evidenced by previous studies, the human activity reduction resulted in lower levels of background seismic vibrations mostly for frequencies ranging between 2 and 20 Hz. As this is also the characteristic frequency band for the body-wave arrivals of local events, we could expect an increase on the signal-to-noise ratio during lockdown, resulting in a better detection of such phases, for seismic stations located in urban environments. The deployment in the city of Barcelona of a large seismic network during the lockdown period provides a unique opportunity to check this hypothesis. A manual picking of the local earthquake arrivals reported in the Institut Cartogràfic i Geològic de Catalunya ICGC catalog has been carried out on the waveforms recorded by the permanent and temporary seismic stations located within the city. We have reviewed the seismic events occurring between December 2019 and September 2020, to compare the detection level in the pre-lockdown, lockdown, and post-lockdown time periods. By quantifying the number of picked P-waves on each station and classifying this information according to the hour of day, it has been possible to analyze the correlation between the human common activity and the capacity of seismic stations to record seismic events. First results indicate that the reduction of seismic noise during lockdown resulted in a higher number of pickings at labor hours. However, the limited number of local events and the occurrence of a small seismicity cluster close to Barcelona during the lockdown, makes it difficult to be conclusive on the influence of the seismic noise reduction on the detection capability.