Title Pre-failure behaviour of an unstable limestone cliff from displacement and seismic data
Author Got, J.; Mourot, P.; Grangeon, J.
Author Affil Got, J., Université de Savoie, Laboratoire de Géophysique Interne et Tectonophysique, Le Bourget-du-Lac, France
Source Natural Hazards and Earth System Sciences (NHESS), 10(4), p.819-829, . Publisher: Copernicus GmbH on behalf of the European Geophysical Society, Katlenburg- Lindau, Germany. ISSN: 1561- 8633
Publication Date 2010
Notes In English. Accessed in Nov., 2010; abstract: doi:10.5194/nhess-10-819-2010. 47 refs. GeoRef Acc. No: 309551
Index Terms cracks; freeze thaw cycles; hydrology; porous materials; slope stability; slopes; temperature; tensile properties; water vapor; weathering; Alps--Vercors; Alps; carbonate rocks; Chamousset Cliff; cliffs; Dauphine Alps; eigenvalues; engineering properties; Europe; France; frost action; limestone; low temperature; microcracks; outcrops; rainfall; rupture; saturation; sedimentary rocks; seismicity; tensile strength; Vercors; Western Alps; Western Europe
Abstract We monitored the displacement and seismic activity of an unstable vertical rock slice in a natural limestone cliff of the southeast Vercors massif, southeast France, during the months preceding its collapse. Displacement measurements showed an average acceleration of the movement of its top, with clear increases in the displacement velocity and in the discrete seismic event production rate during periods where temperature falls, with more activity when rainfall or frost occurs. Crises of discrete seismic events produce high amplitudes in periodograms, but do not change the high frequency base noise level rate. We infer that these crises express the critical crack growth induced by water weakening (from water vapor condensation or rain) of the rock strength rather than to a rapid change in applied stresses. Seismic noise analysis showed a steady increase in the high frequency base noise level and the emergence of spectral modes in the signal recorded by the sensor installed on the unstable rock slice during the weeks preceding the collapse. High frequency seismic noise base level seems to represent subcritical crack growth. It is a smooth and robust parameter whose variations are related to generalized changes in the rupture process. Drop of the seismic noise amplitude was concomitant with the emergence of spectral modes - that are compatible with high-order eigenmodes of the unstable rock slice - during the later stages of its instability. Seismic noise analysis, especially high frequency base noise level analysis may complement that of inverse displacement velocity in early-warning approaches when strong displacement fluctuations occur.
URL http://www.nat-hazards-earth-syst-sci.net/10/819/2010/nhess-10-819-2010.pdf
Publication Type journal article
Record ID 65006556