Ambient Vibration Recordings Used to Map Glaciers Thickness - A First Study from Alpine Glaciers

Microtremor measurements and the Nakamura’s HVSR (Horizontal to vertical spectral ratio) technique, generally used for site-effect studies as well as to determine the thickness of soft sediment layers, can be effectively applied to map the thickness of glaciers. In this work the GPR (ground penetrating radar) and multichannel seismic methods, widely employed to image the earth interior, are applied to validate the HVSR technique on some alpine glaciers: the Pian di Neve glacier on the Adamello massif (Italy), the Forni glacier in the Ortles/Cevedale massif (Italy) and the Aletsch glacier (Switzerland). Comparing the results obtained from the different methods we show that the resonance frequency in the HVSR spectra can be well correlated with the ice thickness at the site, in a wide range from tens of meters to more than 800 m. The application of the passive seismic method on glaciers, requiring less economic and operational efforts, enables to avoid most of the logistical difficulties affecting the GPR and active seismic methods in these extreme environments.