  The Virgo gravitational wave detector is an interferometer (ITF) with 3km
arms located in Pisa, Italy. From July to October 2010, Virgo performed its
third science run (VSR3) in coincidence with the LIGO detectors. Despite
several techniques adopted to isolate the interferometer from the environment,
seismic noise remains an important issue for Virgo. Vibrations produced by the
detector infrastructure (such as air conditioning units, water
chillers/heaters, pumps) are found to affect Virgo's sensitivity, with the main
coupling mechanisms being through beam jitter and scattered light processes.
The Advanced Virgo (AdV) design seeks to reduce ITF couplings to environmental
noise by having most vibration-sensitive components suspended and in-vacuum, as
well as muffle and relocate loud machines. During the months of June and July
2010, a Guralp-3TD seismometer was stationed at various locations around the
Virgo site hosting major infrastructure machines. Seismic data were examined
using spectral and coherence analysis with seismic probes close to the
detector. The primary aim of this study was to identify noisy machines which
seismically affect the ITF environment and thus require mitigation attention.
Analyzed machines are located at various distances from the experimental halls,
ranging from 10m to 100m. An attempt is made to measure the attenuation of
emitted noise at the ITF and correlate it to the distance from the source and
to seismic attenuation models in soil.
