Urban activities cause minute vibrations of the earth surface that can be detected by highly sensitive seismometers. In the island city-state Singapore, human activities have been dramatically changed since April 2020 by government measures to suppress the spread of COVID-19. By analyzing the high- frequency seismic signals, the impact of the pandemic and its corresponding mitigation measures were quantified as traffic flow at the exit of the National University of Singapore (NUS) and at the intersection between Pasir Panjang Port Terminal and West Coast Park, representing activities at nonessential workplaces, essential workplaces, and recreational areas. The anonymity of seismic data enabled an unprecedented spatial and temporal resolution that is pivotal to understand the heterogeneity and evolution of pandemic responses in different sectors of an urban society. The rich information extracted from seismic data provide an opportunity for real time activity monitoring and dynamic policy making in order to ensure a successful pandemic mitigation and a less disturbed urban lifestyle.