Abstract
The changes in the seismic signals generated by avalanches recorded at three sites along a path at the Vallée de la Sionne (VdlS) experimental site are presented. We discuss and correlate the differences in the duration, signal amplitudes, and frequency content of the sections (Signal ONset (ON), Signal Body (SBO), and Signal TAil and Signal ENd STA-SEN) of the spectrograms with the evolution of the powder, transitional and wet snow avalanches along a path. The development of the avalanche front was quantified using the exponential function in time F (t) = K’ exp (β t) fitted to the shape of the signal ONset (SON section of the spectrogram. The speed of the avalanche front is contained in β. To this end, a new method was developed. The three seismic components were converted into one seismic component (FS), when expressing the vector in polar coordinates. We linked the theoretical function of the shape of the FS-SON section of the spectrogram to the numerical coefficients of its shape after considering the spectrogram as an image. This allowed us to obtain the coefficients K’ and β. For this purpose, the Hough Transform (HT) was applied to the image. The values of the resulting coefficients K’ and β are included in different ranges in accordance with the three types of avalanche. Curves created with these coefficients enable us to estimate the development of the different avalanche types along the path. Our results show the feasibility of classifying the type of avalanche through these coefficients. Average speeds of the avalanches approaching the recording sites were estimated. The speed values of wet and transitional avalanches are consistent with those derived from GEODAR (GEOphysical Doppler radAR) measurements, when available. The absence of agreement in the speed values obtained from seismic signals and GEODAR measurements for powder snow avalanches indicates, for this type of avalanche, a different source of the measured signal. Hence, the use of the two measuring systems proves to be complementary.
Highlights
It is well known that snow avalanches generate seismic signals and that they can be used for monitoring e.g., [1,2,3,4,5,6,7,8,9,10,11,12]
New insights were provided by comparing the seismic signals with the results from the measurements of the FCMW radar [24] co-located with a seismic sensor
The spectrogram amplitudes are represented in 10−1 dB and in a GivenFor oura correct interestreading in the estimation of the evolution thereferences avalanche front, we studied the color scale
Summary
It is well known that snow avalanches generate seismic signals and that they can be used for monitoring e.g., [1,2,3,4,5,6,7,8,9,10,11,12]. New insights were provided by comparing the seismic signals with the results from the measurements of the FCMW radar [24] co-located with a seismic sensor. The results of FCMW and of seismic sensors at two strategic sites of the avalanche path, the track zone and the run-out zone, were compared in detail in [19]. A division of the spectrogram into sections corresponding to avalanches approaching a sensor: SON (Signal ONset), SOV (Signal OVer), and SEN (Signal ENd) depending on whether the avalanche approaches the sensor, is over it, or is moving away from it, respectively, was made [19]
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