S. Rosat$^{(a)}$, J. Hinderer$^{(a)}$, D. Crossley$^{(b)}$ and L. Rivera$^{(a)}$
$^{(a)}$IPGS-EOST (UMR CNRS-ULP 7516), 5, rue Descartes, 67084 Strasbourg, France. $^{(b)}$Dept. Earth and Atmospheric Sciences, Saint Louis University, Saint Louis, MO, USA.
Since 1997 a network of superconducting gravimeters (SG) has been monitoring the variations of the Earth's gravity field. Data from the network, under the coordination of the Global Geodynamics Project (GGP), allow a comparison of the noise levels of the different contributing stations in the seismic, subseismic and tidal frequency bands. The analysis of the noise levels at a station leads to Power Spectral Densities of the instrument series. In the seismic band (2-7 mHz) the background free oscillations or "hum" constitute a lower bound for observable signals at any site on the Earth's surface. Spectra of the 2001 Mw=8.4 Peru event at GGP Strasbourg station and GEOSCOPE Echery station enable a comparison of the signal to noise ratio. Knowledge of the noise levels at each station is important in a number of studies that combine the data to determine global Earth parameters. We cite for example the stacking of the data in the search for the gravity variations associated with the translational mode of the inner core. Synthetic signals are used to estimate the possible detection of the Slichter mode with SG data and a stacking method is tested.