Using Seismic Noise Levels to Monitor Social Isolation: An Example From Rio de Janeiro, Brazil

Decrease of seismic noise level, after reduction of traffic due to the COVID-19 pandemic, has been observed worldwide. The possibility of using seismic noise as another proxy to estimate social isolation was tested with a station within Rio de Janeiro city. We used the isolation index measured from smartphone movement to calibrate the seismic noise levels and estimated an Isolation Seismic Index,ISI(% of the population at home), using the seismic noise energy. Noise levels best correlate with isolation measures in the frequency range 4-8 Hz. Small differences between the smartphone and theISIindexes are interpreted as differences in social activities and noise sources. All mobility indexes are proxies to the actual isolation. AlthoughISIdoes not measure the number of people outside, it measures the number of noise sources (vehicles, trains, factories, etc.) and can be used as additional information to interpret anomalies in other proxies.