Monitoring human activity at a very local scale with ground motion records: the early stage of COVID-19 pandemic in California, USA, New York City, USA, and Mexicali, Mexico

Abstract:

In the global coronavirus (COVID-19) pandemic, governments around the world took different levels of social distancing measures to slow down the spread of the virus, and human activity worldwide slowed down considerably. In this study, we analyze the change in cultural seismic noise level, which we refer to as the Human Activity Index (HAI) through a survey of seismic stations in California, USA, New York City, USA, and Baja California, Mexico from early December, 2019 to late April, 2020.

Some stations recorded a drop in the HAI during the COVID-19 pandemic and the timing of the drop typically correlates with the timing of a strict curtailment of personal and economic activity issued by the local government. In other locations, the drop in the HAI appears to be influenced by other regional factors. At stations LD-CPNY in Central Park, New York City, USA, the decrease in cultural noise recorded by the seismic station occurs after the drop in activity observed in smartphone-based mobility metrics of the whole city, reflecting the possibility that people continued to frequent Central Park even after other non-essential activities ceased. At BC-UABX in downtown Mexicali, Baja California, Mexico, the cultural noise is better correlated with the “stay-at-home'' order in the neighboring state of California, USA than the “stay-at-home'' order of the local government in Mexico, suggesting a potential geographical control on human activity instead of a political control. We also found many stations that did not record a drop during the early stage of COVID-19 epidemic. Of the 19 stations of the Southern California Seismic Network that were surveyed, we find that only five show a similar extent of drop in the HAI comparable to the Christmas holiday in 2019. This suggests that human activity such as traffic or industry tied to essential businesses, did not reduce during the COVID-19 pandemic in Southern California.

Our results show that the cultural noise recorded by seismic stations is capable of being used as a Human Activity Index and that this metric is particularly powerful in measuring how localized communities responded to the COVID-19 pandemic. Its potential to carefully monitor cultural activity with seismic methods may have benefits to scientists and policy makers interested in understanding human responses to a pandemic.