The mechanical properties of snow and ice of an alpine glacier inferred by integrating seismic and GPR methods

Ground penetrating radar (GPR) and seismic survey have been performed on a glacier in the Italian Alps to characterize the uppermost layers of the snow-ice transition zone. This issue is relevant in the detection of the mechanical properties (density, bulk and shear modulus) during the thermo-mechanical transformation from seasonal snow to pure ice. The integration of GPR, P-wave seismic data and dispersive seismic surface wave was focused to derive the snow density and the bulk and shear modulus. The mechanical properties of the snow and ice zone to a depth of about 25-30 m are estimated. We found a gradual increase of the seismic wave velocities with depth indicating an improvement of the mechanical properties, mostly related to the densification process of the snow for sintering mechanism. The bulk modulus ranges from about 1 GPa at 5 m of depth to about 10-10.5 GPa at 25 m; the shear modulus ranges from about 0.4 to 1.7 GPa. The Poisson ratio (maximum 0.4) is slightly higher than those commonly reported in the literature on laboratory results. A good agreement between the radar estimated density and the value inferred by the interpretation of seismic data is achieved. The integration of GPR and seismic survey methods allows one to infer information on layering and mechanical properties of the uppermost part of the glacier up to a depth of about 20 m.