Long term seismic noise acquisition and analysis in the Homestake mine with tunable monolithic sensors

In this paper we present and discuss the scientific data taken by two mechanical monolithic horizontal sensor prototypes located at the 2000 ft deep level in the Homestake mine (South Dakota, USA). The main goal of this experiment was to provide a preliminary characterization of the Homestake site in the frequency band 10^-4 ÷ 30 Hz, necessary to evaluate the feasibility of underground gravitational-wave interferometers sensitive at 1 Hz and below, and to test the sensor prototypes in the band (10^-6 ÷ 30 Hz). The first results show the good performances of the sensors, being they able both to detect the Peterson Low Noise Spectrum and, in the very low frequency region, the peaks due to Earth tides, although configured with a limited sensitivity (resonance frequency of ≈ 300 mHz and optical lever readout).