Using Seismic Noise to Monitor COVID-19 Societal Response in Halifax

Abstract

Seismometers record signals from more than just earthquakes. Cultural noise, high-frequency seismic noise generated from human activities (e.g., traffic) produces a distinct diurnal signature in frequencies above 1 Hz due to how human activities change from day to night. To mitigate the spread of the coronavirus disease (COVID‐19), public health regulations were imposed worldwide leading to an unprecedented global quieting in the seismic record. This unlocked a new pathway to explore the effects of anthropogenic activity on seismic noise. Cultural noise was analyzed in the month leading to and following the initial 2020 lockdown measures in Halifax, Nova Scotia, Canada, then compared with baseline data established from the year prior. Immediately following the lockdown, cultural noise (10-14 Hz) in Halifax dropped by 11.85% from the month prior. In comparison to 2019, seismic power had dropped by 17.19%. This suggests the pandemic itself, prior to lockdown measures, influenced human activities. In addition, annual holidays, such as Easter weekend and the tragic Nova Scotia Massacre, led to a reduction in seismic power relative to that of the initial lockdown. Overall, a correlation between cultural noise and human activity was found. Seismic data indicate that human activity decreased a fraction of that reported from major cities around the world, displaying how different municipalities can react to lockdown conditions. This study demonstrates the use of seismic cultural noise analysis as an independent way to quantify human mobility under government-mandated restrictions. Keywords: cultural noise, COVID-19, signal processing, lockdown, computational seismology