Caractérisation de la structure interne et de l'état hydrique de glissements argilo-marneux par tomographie géophysique : l'exemple du glissement-coulée de Super-Sauze (Alpes du Sud,France)

Geophysical methods such as seismic surveying and electrical resistivity imaging appear to be well-adapted to investigate and understand landslide mechanisms. They allow direct and non-intrusive measurement of acoustic velocity and electrical resistivity, two fundamental parameters used to define the physical properties of the reworked moving materials. Both methods were applied at the Super-Sauze site in the French South Alps, where a typical example of an intra-material earthflow-mudslide can be observed. Measurements were taken simultaneously along two orthogonal profiles: one 325 m in length is perpendicular to the axis of the earthflow; the other 235 m in length is located along the axis of the earthflow. The results show a correlation between the seismic and electrical resistivity data, confirming that the simultaneous use of both methods gives complementary information about landslide mechanisms. The seismic data provide information on fracture density variations, whereas the electrical resistivity data provide information on water content variations. To cite this article: G. Grandjean et al., C. R. Geoscience 338 (2006).     

Landslide kinematics inferred from in situ measurements: the Cliets rock-slide (Savoie,French Alps)

This paper presents an analysis of two large rock toppling/sliding events which occurred in January 2014 and February 2019 at the Cliets unstable slope (Savoie, French Alps). To understand the mechanism involved and its control by external forcings, a multi-technique analysis approach is used combining geological observations, meteorological data analysis, topographic measurements and simple physical modeling. The pre-failure stage of the events is more particularly analyzed. No direct relationships are found between triggering factors and surface motion though a kinematics analysis highlights the transition toppling-sliding. It showed that, at first order, this transition occurred 4 years before the first failure of 2014, while it happened 2 months before the second failure of 2019. From this date, the environment is considered like a block sliding on an inclined plane. By applying a frictional model (Helmstetter et al. in Journal of Geophysical Research: Solid Earth 109(B2), 2004), we illustrated that the two events belong to an unstable velocity-weakening sliding regime. The time to failure (Voight in Science 243(4888):200–203, 1989) is forecasted with the model, and the results are consistent with the observations. They confirm that the gravitational factor is predominant over the triggering factors for the two events.