Sardinia's seasonal seismic calm bodes well for Einstein Telescope

Three years of borehole seismic data from Sardinia reveal that winter and summer represent the worst and best noise conditions, respectively, but the gap between them is narrow. Converting those measured spectra into Newtonian noise estimates and revised sensitivity curves, the authors find that binary neutron star and intermediate-mass black hole signal-to-noise ratios shift by just a few percent between seasons. This stability holds even before applying noise-subtraction techniques, which would shrink the effect further. The results support Sardinia as a viable host for ET's demanding low-frequency science goals.