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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/esurf-2019-61
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2019-61
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 18 Nov 2019

Submitted as: research article | 18 Nov 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).

Seismo-acoustic energy partitioning of a powder snow avalanche

Emanuele Marchetti1, Alec van Herwijnen2, Marc Christen2, Maria Cristina Silengo1, and Giulia Barfucci1 Emanuele Marchetti et al.
  • 1Department of Earth Sciences, University of Firenze, Firenze, Italy
  • 2WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland

Abstract. While flowing downhill, a snow avalanche radiates seismic waves in the ground and infrasonic waves in the atmosphere. Seismic energy is radiated by the dense basal layer flowing above the ground, while infrasound energy is likely radiated by the powder front. However, the mutual energy partitioning is not fully understood. We present infrasonic and seismic array data of a powder snow avalanche, that released on 5 February 2016, in the Dischma valley above Davos, Switzerland. A five element infrasound array and a seven element seismic array were deployed at short distance (< 500 m) from each other, and close (< 1500 m) to the avalanche path. The avalanche dynamics was modeled by using RAMMS, and characterized in terms of front velocity and flow height. The use of arrays rather than single sensors, allowed us to increase the signal-to-noise ratio, and to identify the event in terms of back-azimuth and apparent velocity of the recorded wave-fields. Wave parameters, derived from array processing, were used to identify the avalanche path and highlight the areas, along the path, where seismic and infrasound energy radiation occurred. The analysis showed that seismic energy is radiated all along the avalanche path, from the initiation to the deposition area, while infrasound is radiated only from a limited sector, where the flow is accelerated and the powder cloud develops. Recorded seismic signal is characterized by scattered back-azimuth, suggesting that seismic energy is likely radiated by multiple sources acting at once. On the contrary, infrasound signal is characterized by a clear variation of back-azimuth and apparent velocity. This indicates that infrasound energy radiation is dominated by a moving point source, likely consistent with the powder cloud. Thanks to such clear wave parameters, infrasound revealed particularly efficient for avalanche detection and path identification. While the infrasound apparent velocity decreases as the flow moves downhill, the seismic apparent velocity is quite scattered, but it lowers down to sound velocity during the phase of maximum infrasound radiation. This indicates an efficient process of infrasound to seismic energy transition, that, in our case, increases ≈ 20 % the recorded seismic amplitude. Such an effect can be accounted for when avalanche magnitude is estimated from seismic amplitude. Presented results clearly indicate how the process of seismo-acoustic energy radiation by a powder avalanche is very complex, and likely controlled by the powder cloud formation and dynamics, and is hence affected by the path geometry and snow characteristics.

Emanuele Marchetti et al.
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Data sets

off_davos.mat E. Marchetti, A. van Herwijnen, M. Christian, M. C. Silengo, and G. Barfucci https://doi.org/10.17605/OSF.IO/P28GC

Video supplement

ChleinSattelhorn.mp4 E. Marchetti, A. van Herwijnen, M. Christian, M. C. Silengo, and G. Barfucci https://doi.org/10.17605/OSF.IO/P28GC

Emanuele Marchetti et al.
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Short summary
We present infrasonic and seismic array data of a powder snow avalanche, that released on 5 February 2016, in the Dischma valley nearby Davos, Switzerland. Combining information derived from both arrays we show how infrasound and seismic energy are radiated from different sources acting along the path. Moreover, infrasound transmits to the ground and affect the recorded seismic signal. Results highlight the benefits of combined seismo-acoustic array analyses, for monitoring and research.
We present infrasonic and seismic array data of a powder snow avalanche, that released on 5...
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