Abstract
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. 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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