Deducing avalanche size and flow regimes from seismic measurements

Abstract

The ground motion generated by a snow avalanche is a complex natural phenomenon produced by the interaction of the avalanche with the snow cover and the terrain. Nowadays, avalanches are recorded using seismic sensors that provide data that can be used to obtain information about the characteristics of the source (type of flow regime), the basic dynamic processes (erosion and deposition) and the approximate size of the avalanche. In order to better understand the connection between seismic signals and avalanche dynamics, we analysed data from thirty avalanches at the Vallée de la Sionne test site in Switzerland. Seismic sensors were configured linearly both in and outside the avalanche path. For each seismic signal, the duration, peak ground velocity of the envelope, and both the intensity and the frequency content were compared with the avalanche flow regimes and the thicknesses of the snow cover measured using frequency-modulated continuous wave radar, as well as with the avalanche run-out distances obtained from photographs. We showed that the frequency content of the seismic signal can be used to infer the avalanche flow regime and to distinguish between dense and energetic turbulent flows. Furthermore, the seismic signal duration of both dense and energetic flows can be correlated to avalanche run-out distance. If the snow cover at the seismic sensor location is less than approximately 2m and energy absorption does not significantly weaken the intensity of the signal, the avalanche run-out distance can also be deduced from the peak ground velocity and its intensity. These results suggest that the flow type characteristics and the run-out distances of avalanches can be feasibly inferred using only seismic data. Such analysis of seismic data can be usefully employed in avalanche monitoring and management.