I calculated the theoretical sensitivity of the geophones used in SR2:

• Geophones names: 4, 5 and 6.
• The measured and calculated sensitivities are shown in the first screenshot. The noise is higher than expected.
• The numerical data of the geophones sensitivities is not available, so I took them from the plots using WebPlotDigitizer.
• At 200 mHz, the measured values are higher than expected by the following factors:
  • GEO4: 2.7
  • GEO5: 3.7
  • GEO6: 4.7
• The plot also shows the IP-L free swing displacement measured with the geophones on a day with good weather. It was measured by Terrence and Lucia on the 20th of July 2020 (klog 14790 maybe).
• The second screen shot shows the noise budget of GEO4 as an example. The dominant contribution is the pre-amplfier noise.
• The third screenshot shows a comparison of two different pre-amplfier calculations and a measurement. The three are consistent.
• I used this reference: Blom, M. (2015). Seismic Attenuation for Advanced Virgo: Vibration Isolation for the External Injection Bench [Phdthesis]. Vrije U., Amsterdam, page 152.

I will add measurements of the IP free swing spectra measured by individual geophones when the micro-seismic is low.