Seismic noise characterization for the Buddusò–Ala dei Sardi wind park (Sardinia, Italy) and its impact on the Einstein Telescope candidate site

Wind turbines generate considerable seismic noise
and interfere with sensitive instruments, such as permanent
and temporary seismic sensors installed nearby, hampering
their detection capabilities. This study investigates the seis-
mic noise emission from one of Italy’s largest wind farms,
consisting of 69 turbines (2 MW each), located in northeast-
ern Sardinia. Characterizing the noise emission from this
wind farm is of particular importance due to its proximity
to the Italian candidate site for hosting the Einstein Tele-
scope (ET), the third-generation observatory for gravitational
waves. We run a passive seismic experiment, “Wind turbIne
Noise assEsSment in the Italian site candidate for Einstein
Telescope” (WINES), using a linear array of nine broadband
stations, installed at increasing distances from the wind farm.
Spectral analysis, based on the retrieval of spectrograms and power spectral densities at all stations, shows a significant in-
crease in noise amplitude when the wind farm is in operation.
The reconstruction of noise polarization points out that the
noise wavefield originates from a direction consistent with
the wind farm’s location. We recognize four dominant fixed
spectral peaks at 3.4, 5.0, 6.8, and 9.5 Hz, corresponding to
the modes of vibration of the wind turbine towers. While de-
creasing in amplitude with distance, the 3.4 Hz peak remains
detectable up to 13 km from the nearest turbine. Assuming an
amplitude decay model of the form r−α, where r is the dis-
tance, we estimate a damping factor of α∼2, which remains
rather constant for each of the four main peaks, an observa-
tion that we relate to the good geomechanical characteristics
of the local terrain, consisting of granitoid rocks. To better
evaluate the possible impact of the wind farm noise emission on the ET, we also analyze the seismic data from two per-
manent stations bordering the ET candidate site area, each
equipped with both a surface sensor and a borehole sensor at
approximately 250 m depth. Power spectral density analysis
for the surface and borehole sensors exhibits similar results
and very low noise levels. When the wind farm operates at
full capacity, the borehole sensors show an effective noise
suppression at depth in the frequency range of interest (1–
10 Hz). However, small residual spectral peaks at 3.4 Hz and
between 4–6 Hz remain detectable.