Pre-failure behaviour of an unstable limestone cliff from displacement and seismic data

Abstract

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 sliceduring the later stages of its instability. Seismic noise analysis, especially high frequency base noise level analysis may complement that of inverse displacement velocity in earlywarning approaches when strong displacement fluctuations occur.

Seismic monitoring of precursory fracture signals from a destructive rockfall in the Vorarlberg Alps, Austria

“…Studies of seismic monitoring of soft rock-landslides were conducted at the Heumoes slope, Austria Joswig, 2008, 2009;Walter et al, 2011), at the mudslide in Super-Sauze, French Alps (Walter et al, , 2011, and at the Slumgullion landslide, Colorado, US (Gomberg et al, 1995(Gomberg et al, , 2011. The most similar studies to ours documented in the literature are the ones of Got et al (2010) and Levy et al (2011). In these studies the locations of possible rock collapse were well known and therefore the area of interest has been instrumented satisfactorily with dense seismic and geotechnical stations.…”

“…On a much smaller scale, fracture processes on landslides, with magnitudes of M L < 0.0, were observed in several studies by advanced seismic monitoring technics. Fracture processes on landslides consisting of hard rock (fragments) were monitored by, for example, Brückl and Mertl (2006) in the Austrian Alps, Spillmann et al (2007) in the Swiss Alps, Helmstetter and Garambois (2010) at a rockslide, Got et al (2010) and Levy et al (2011) at rock columns, both in the French Alps, and Roth et al (2005) at the Aknes fjord in Norway. Studies of seismic monitoring of soft rock-landslides were conducted at the Heumoes slope, Austria Joswig, 2008, 2009;Walter et al, 2011), at the mudslide in Super-Sauze, French Alps (Walter et al, , 2011, and at the Slumgullion landslide, Colorado, US (Gomberg et al, 1995(Gomberg et al, , 2011.…”

Measuring and localizing acoustic emission events in snow prior to fracture

“…In other quasi-brittle materials such as concrete (Ohtsu, 1996) or wood (Bucur, 2006) the AE technique is commonly used to study and predict failure processes (Johansen and Sornette, 2000). In the field of natural hazards, acoustic signals have been used to investigate earthquake occurrence (Niccolini et al, 2011) and to predict the collapse of a limestone cliff (Amitrano et al, 2005;Got et al, 2010). Girard et al (2012) set up an acoustic sensor network in order to predict failure within rocks and permafrost.…”

Evaluation of damage level for rock slopes using acoustic emission technique with waveguides

“…Therefore, signal discrimination and noise reduction are extremely important for the successful application of AE techniques. Despite these limitations, AE monitoring techniques have been successfully applied to rock damage evaluation in some cases (Ishida, 1999;Morioka et al, 2004;Cai et al, 2007;Wang and Ge, 2008) and prediction of the failure in slopes (Amitrano et al, 2005Guglielmi et al, 2008;Senfaute et al, 2009;Gaffet et al, 2010;Got et al, 2010;Helmstetter and Garambois, 2010). However, most of them have applied to the natural slopes or cliffs using geophones or accelerometers instead of AE sensors.…”