Reduction of high frequency seismic noise in and around Wuhan city due to the COVID-19 lockdown

Abstract:

Ambient noise observation is important in pure and applied geophysics, as it offers better understanding of earth structures, detailed geodynamic environments, and environment changes (ice quake) as well. Continuous ambient noise studies in seismology, have greatly advanced our understanding of detailed structure in tectonically active areas. In recent years, there has been an increasing trend towards footbridge vibration produced by human-induced loads (Fujino et al., 1993, Caetano et al. (2010)), human-induced floor vibrations (Toratti and Talja, 2006, Lu et al., 2012)， and seismic noise reduction due to the COVID-19 pandemic lockdowns (Lecocq et al., 2020).

In this work, we systematically analyzed the intensities of the high frequency seismic noises (over 1 Hz) using continuous seismic data that were recorded in and around Wuhan city, China from the year 2019. The seismic network consists of 12 broadband seismometers that are permanently deployed in the Wuhan area with station intervals of ~50 km. We calculate the Power Spectrum Density and Power Density Functions of the three components at each station. The results show clear reduction of the maximum displacements at high frequency bands. Those obvious drops are correlated with the lockdown of the Wuhan city, indicating a close correlation between the intensity of human activity and high frequency seismic noise.

By correlating the intensity variation of the ambient noise and the intensity of human activities, there might be a way to evaluate/reveal the characteristics of human activity seismically. It will potentially impact the public management and crisis operations in urban areas, as well as its benefits for seismic observations in site selection, data interpretation, and de-noising operations.