The containers of the geophones, made of stainless steel tubes sealed with CF-100 flanges, turned out rather large and heavy, with about 10kg each. The original plan included using pre-amplifiers for the geophones placed inside the cans. The plots in figure F.2 show a rough comparison of the vertical geophone performances in three different configurations, connecting the pre-amplifiers directly to the geophone (local) or using shielded twisted pair cables, 12m and 2 × 24m (remote). In both remote pre-amplifier configurations the cable shield was only connected to the GND lead at the pre-amplifier input; the sensing coil as well as the geophone case were left floating. The comparison was done by setting up two nominally identical geophones and measuring the coherence spectrum between them. In conclusion, no significant or traceable difference has been observed between the different set-ups.