Monitoring of snow avalanches using a seismic array: Location, speed estimation, and relationships to meteorological variables
Lacroix, P. ; Grasso, J.-R. ; Roulle, Jacques ; Giraud, Gérald ; Goetz, Daniel ; Morin, Samuel ; Helmstetter, A.
Monitoring snow avalanches is necessary in order to better understand their triggering mechanisms and ultimately improve forecast performance. Seismic monitoring has been developed by several groups over the last 20 years and holds great potential to detect, locate, and characterize snow avalanches. During the 2009-2010 winter, a seismic antenna was installed in the French Alps close to the village of Saint-Christophe-en-Oisans (1700 m above sea level). The array of seven sensors operated during 50 days in October and November 2009 under snow-free conditions and during 40 days in January and February 2010 in presence of snow. It recorded different types of seismic events including snow avalanches, rockfalls, shots, and regional and local microearthquakes. Eighty avalanche signals were visually identified. Using a beam-forming method, we were able to locate snow avalanches on slopes of various orientations in a radius of about 3 km and track their propagation. The location technique allowed for the estimation of avalanches' front speed, which ranged between 12 and 32 m s?1. The method can also distinguish dry and wet snow avalanches. Durations of avalanches can be as long as 380 s because of the length of the slopes in the area. Seismic monitoring provides a catalog of avalanches with precise times, which can be used to analyze the impact of meteorological forcings on the avalanche triggering. Snowfall is found to be the dominant forcing of avalanche activity during this period, as revealed by the strongest correlation. For the period of study, our results suggest that the impact of precipitation on the snowpack instability lasts for about 6 days.
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