On the characterization of seismic signals generated by snow avalanches for monitoring purposes

Abstract

Seismic signals from artificially released avalanches were studied in an attempt to characterize them for avalanche-monitoring purposes. The seismic signals generated by different sizes and types of avalanches were recorded and analyzed in the time and frequency domains. Synchronized recordings of the corresponding seismic signals and the video images of the evolution of the avalanches were obtained together with a detailed cartography. Characteristic signatures in the frequency and time domains were found to depend on the characteristics of the avalanche path and measuring location, but to be mostly independent of avalanche size. The source of the different parts of the recorded seismic signals was determined. A relationship was observed between the avalanche size and the amplitude of the signals. Given the presence of local site effects, a prior seismic characterization of the avalanche path in relation to the recording sites is necessary for monitoring purposes. Moreover” it was found that sliding slabs in the early phase of acceleration produce little seismic energy, resulting in a time lapse between the observable start of the avalanche and the arrival of the detectable seismic waves at the receiving station.

Insights into rock‐ice avalanche dynamics by combined analysis of seismic recordings and a numerical avalanche model

“…If three‐component seismic data are available within a short distance from the source, calculations of the total received energy might be more representative than only horizontally polarized signals. However, many stations still record only vertical components, and Suriñach et al [2001] have shown that the absolute amplitudes in three‐component signals can be different, while seismic energy and frequency content are similarly distributed. Because our analysis is based only on the shape of the seismograms (amplitude envelopes, Figures 3 and 5) and not on the magnitudes, the vertical component should sufficiently well represent the information needed for comparison with modeling results.…”

“…Seismic source signal: This is the seismic signal produced by the avalanche directly at the site of the event. The strength of the produced signal is related to the total momentum, respectively total kinetic energy of the avalanche (which in turn depend on mass and velocity, and hence also on entrainment [ Suriñach et al , 2001, 2005]). Furthermore, the production of seismic energy is affected by the surface properties of the avalanche path which include surface roughness (on a millimeter to decameter scale), but also centrifugal and impact effects caused by minor and major obstacles, topographic steps and lateral deflections [ McSaveney and Downes , 2002; Sabot et al , 1998; Suriñach et al , 2001].…”

“…The strength of the produced signal is related to the total momentum, respectively total kinetic energy of the avalanche (which in turn depend on mass and velocity, and hence also on entrainment [ Suriñach et al , 2001, 2005]). Furthermore, the production of seismic energy is affected by the surface properties of the avalanche path which include surface roughness (on a millimeter to decameter scale), but also centrifugal and impact effects caused by minor and major obstacles, topographic steps and lateral deflections [ McSaveney and Downes , 2002; Sabot et al , 1998; Suriñach et al , 2001]. All these components control the rate at which kinetic energy is transformed into heat, particle fragmentation [ Crosta et al , 2007; Davies et al , 2007; Locat et al , 2006] and seismic waves.…”

“…While station EWZ recorded only the vertical component of ground shaking, more distant stations were three‐component (Figure 4). These stations show roughly equal amplitudes on all channels, suggesting that analysis of the vertical component at EWZ (and ILS for Iliamna) is a reasonable proxy for the total ground motion; however, some differences in amplitudes between horizontal and vertical components cannot be excluded [see also Suriñach et al , 2001]. The impacts of the avalanche on the topographic steps have generated bursts of high‐frequency seismic energy which were more rapidly attenuated with increasing distance than the low‐frequency signal portion.…”

Numerical modeling of landquakes

“…and of its dynamics and mechanical behaviour (velocity, friction coefficient, etc.) [ Suriñach et al , 2001; Brodsky et al , 2003; La Rocca et al , 2004; Vilajosana et al , 2007; Huggel et al , 2007; Deparis et al , 2008; Cole et al , 2009].…”