  Mixed space-time spectral analysis was applied for the detection of seismic
waves passing through the west-end building of the Virgo interferometer. The
method enables detection of every single passing wave, including its frequency,
length, direction, and amplitude. A thorough analysis aimed to improving
sensitivity of the Virgo detector was made for the data gathered by 38 seismic
sensors, in the two-week measurement period, from 24 January to 6 February
2018, and for frequency range 5--20 Hz. Two dominant seismic-wave frequencies
were found: 5.5 Hz and 17.1 Hz. The possible sources of these waves were
identified, that is, the nearby industrial complex for the frequency 5.5 Hz and
a small object 100 m away from the west-end buiding for 17.1 Hz. The obtained
results are going to be used to provide better estimation of the newtonian
noise near the Virgo interferometer.
