  Seismic noise with frequencies above 1 Hz is often called cultural noise and
is generally correlated quite well with human activities. Recently, cities in
mainland China and Italy imposed lockdown restrictions in response to COVID-19,
which gave us an unprecedented opportunity to study the relationship between
seismic noise above 1 Hz and human activities. Using seismic records from
stations in China and Italy, we show that seismic noise above 1 Hz was
primarily generated by the local transportation systems. The lockdown of the
cities and the imposition of travel restrictions led to a ~4-12 dB energy
decrease in seismic noise in mainland China. Data also show that different
Chinese cities experienced distinct periods of diminished cultural noise,
related to differences in local response to the epidemic. In contrast, there
was only ~1-6 dB energy decrease of seismic noise in Italy, after the country
was put under a lockdown. The noise data indicate that traffic flow did not
decrease as much in Italy, but show how different cities reacted distinctly to
the lockdown conditions.
