Shallow Seismic on Top of the European Roof – A Vibroseismic Experiment on Firn and Ice at Colle Gnifetti

In the summer season 2010, a small shallow reflection seismic experiment was carried out on the firn and ice cover of the Colle Gnifetti, Monte Rosa group, Swiss/Italian Alps. At this site, the physical properties of ice are similar to polar regions, wherefore it is widely used for testing. The challenging experiment in 4500 m asl was designed to explore the scope of shallow vibroseis for seismic targets within and below the firn and ice mass. The small ElVIS vibrator system was used to generate shear waves and compression waves for SH-wave and P-wave receiver setups of two profiles. The resulting sections clearly show the boundary from ice to rock and deeper structures. The deepest features are estimated to 150 m for the SH-wave and 220 m for the P-waves. Reflections could be detected within the ice overburden, which are preliminarily interpreted as change of the crystal structure in the ice column. Furthermore, elastic parameters could be derived from seismic velocities, due to the clear basement reflections. The results of this unique experiment enable new insights in the internal structure of ice formations, and open a promising new investigation method for sub-ice structures and properties, such as basal sediments.