ABSTRACT. Microtremor measurements and the horizontal-to-vertical spectral ratio (HVSR) technique, generally used for site effect studies as well as to determine the thickness of soft sedimentary layers, can effectively be applied to map the thickness of glaciers. In this work the radio-echo sounding, geoelectric and active seismic methods, widely employed to image the earth interior, are applied to verify the reliability of the HVSR technique in Alpine and Antarctic glacial environments. The technique has been used to analyze passive seismic data from glaciers of the Adamello and Ortles-Cevedale massifs (Italy), the Bernese Oberland Alps (Switzerland) and from the Whillans Ice Stream (West Antarctica). Comparing with the results obtained from the different geophysical imaging methods, we show that the resonance frequency in the HVSR spectra correlates well with the ice thickness at the site, in a wide range from a few tens of meters to more than 800 m. The reliability of the method mainly depends on the coupling of sensors at the glacier surface and on the basal impedance contrast. This passive seismic technique offers a logistically efficient and cost effective method to map glacier and ice-sheet thicknesses. Moreover, under certain conditions, it allows reliable estimations of the basal seismic properties.

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[1] We demonstrate that it is possible to retrieve geometric and kinematic information about the source of a destructive past earthquake by inverting its regional macroseismic intensity patterns. In fact, in the case study the inversion results agree with the seismological instrumental measurements of the 1930s and with neotectonic evidence. This leads to the hope that more knowledge about preinstrumental events can be obtained: a key toward improving the calculation of seismic hazard, mostly in the Old World. After validating our technique on the 1987 Whittier Narrows, California, earthquake Gentile et al., 2004] we achieve the present results by investigating an earthquake that happened in 1936 in northeast Italy. The automatic inversions were performed by using a simplified formula for body waves that radiate from a linear source. The inversion shows two minima on the hypersurface of the minimum residuals (calculated -observed intensity at all sites) in the multiparameter model space. These two minimum variance source models resemble the two auxiliary planes of the same theoretical fault plane solution, similar to that given by the standard use of the first P wave arrivals. The present result encourages us to treat more cases and to explore new inversion techniques for quantitatively treating the intensity patterns of earthquakes because, at least in some cases, they carry geometric and kinematic information about their source.

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