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| Titel |
Characterisation of rockfalls from seismic signal: insights from laboratory experiments |
| VerfasserIn |
Maxime Farin, Anne Mangeney, Renaud Toussaint, Julien de Rosny, Nikolai Shapiro, Thomas Dewez, Clément Hibert, Christian Mathon, Olivier Sedan, Frédéric Berger |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108675
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| Publikation (Nr.) |
 EGU/EGU2015-8441.pdf |
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| Zusammenfassung |
| Rockfalls, debris flows and rock avalanches represent a major natural hazard for the
population in mountainous, volcanic and coastal areas but their direct observation on the field
is very difficult. Recent field studies showed that gravitational instabilities can be detected,
localized and characterized thanks to the seismic signal they generate. Therefore, a burning
challenge for risks assessment related to these events is to obtain quantiative informations on
the characteristics of the rockfalls (mass, speed, extension,...) from the properties of the
signal (seismic energy, frequencies,...).
Using a theoretical model of viscoelastic impact of a sphere on a plane, we develop
analytical scaling laws relating the energy radiated in elastic waves, the energy dissipated in
viscoelasticity during the impact and the frequencies of the generated seismic signal to the
mass m and the impact speed V z of the sphere and to the elastic parameters of the involved
materials. The radiated elastic energy is shown to vary as m5/3V z11/5 on plates and as
mV z13/5 on blocks, regardless of the elastic parameters. The energy dissipated in
viscoelasticity does not depend on the support thickness and varies as m2/3V z11/5.
The mean frequency of the generated signal is inversely proportional to the impact
duration.
Then, we conduct simple laboratory experiments that consist in dropping spherical beads
of different size and materials and small gravels on thin plates of glass and PMMA and rock
blocks. In the experiments, piezoelectric accelerometers are used to record the signals in a
wide frequency range: 1 Hz to 56 kHz. The experiments are also monitored optically using
fast cameras. The elastic energy emitted by an impact on the supports is first quantitatively
estimated and compared to the potential energy of fall and to the potential energy change
during the shock. We observe a quantitative agreement between experimental data and
the analytical scaling laws, even when we use small gravels instead of spherical
beads as impactors. These experiments allows to valid the theoretical model and to
establish the energy budget of an impact. The established scaling laws are also
tested for real scale experiments of boulders impacts conducted in Tahiti, French
Polynesia.
Empirical scaling laws are finally established to relate the dynamics and the initial
parameters (mass, aspect ratio i.e., height over length, and bead diameter) of granular flows
with the metrics of the generated seismic signal. |
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