HR: 17:15h
AN: H44A-06    [Abstracts]
TI: Potential of the seismic monitoring for the understanding of gravitational instabilities
AU: * Amitrano, D
EM: amitrano@mines.inpl-nancy.fr
AF: Laego-INPL, School of Mines, Parc de Saurupt, Nancy, 54042 France
AU: Senfaute, G
EM: senfaute@mines.inpl-nancy.fr
AF: Laego-INERIS, School of mines, Parc de Saurupt, 54042, 54042 France
AU: Grasso, J
EM: grasso@moho.ess.ucla.edu
AF: LGIT, Grenoble Observatory, Also at USGS Menlo Parc, J. Fourier University, Grenoble, 38041 France
AU: Got, J
EM: Jean-Luc.Got@univ-savoie.fr
AF: LGIT, Chambery, University of Savoie, Technolac, Chambery, 73000 France
AU: Gaffet, S
EM: gaffet@geoazur.unice.fr
AF: Geoscience Azur, Sofia Antipolis, Valbonne, 06560 France
AU: Clement, C
EM: Cecile.Clement@mines.inpl-nancy.fr
AF: Laego-INERIS, School of mines, Parc de Saurupt, 54042, 54042 France
AB: The macroscopic deformation of rocks, for scales ranging from that of laboratory sample (cm) to that of the rock massive and earth crust, is associated to local irreversible processes (cracks/faults propagation and shearing). These fast movements involve acoustic wave's propagation, which can be observed by remote sensing. Thus, the seismic monitoring during the strain progression can help to a better understanding of rock behaviour and can lead to the determination of failure precursors. Despite of this strong comprehensive potential, this observational tool has not been often used for the study of gravitational instability. Here we present seismic monitoring data's concerning rock slopes instability of size ranging from 103 m3 (cliffs of Mesnil-Val in north-western France, and Valabres south-eastern France) to 50.106 m3 (Deep seated instabilities of ``La ClapiŠre'', and ``Les Ruines de S‚chilienne'', both located in the French Alps). In a general manner, these results show that recordable seismicity exists in the frequency range of 1 Hz to 10 kHz, associated with the rock material deformation. In the case of deep seated instability, we observed large fluctuations of the seismic activity which appear to be related to the seasonal variations of the displacement velocity measured at the slope surface. At the lower scale of the two cliffs studied here, we observed behaviours that could be proposed as candidate for precursors of collapse. For the first case, we observed a huge increase of the seismic activity few hours before a collapse. The seismic rate increase was several magnitude orders larger than the mean seismic activity what permits us to propose this increase as a precursor of the collapse. In the second case, the location of seismic sources permits to identify active deformation zones corresponding to rock mass discontinuities directly observable on the cliff surface. These results indicate the zones on which the failure may occur in the future. This should be verified in the case of a collapse occurs, if any. Overall, these results show the strong potential of the seismic monitoring for reaching a better knowledge of the mechanisms of rock masses deformation and of gravitational instabilities. The determination of operational failure precursors basing on the seismic monitoring is not yet reached but is a major target of this research.
DE: 7223 Seismic hazard assessment and prediction
DE: 7294 Instruments and techniques
DE: 5104 Fracture and flow
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting