Guillaume Chambon

Are stress distributions along faults the signature of asperity squeeze

[1] We propose a possible model for the origin of the spatial fluctuations of the stress field along faults and test our model in the case of the Nojima fault, Japan where unique estimates of the absolute stress field have been obtained. The model consists of two parts: an up-scaling of the fault morphology measured at laboratory scales and a numerical computation using a boundary element approach of the influence on the stress field along the fault of an elastic squeeze of the fault asperities. Accordingly, fluctuations of the stress field along the fault would be dominated by quenched fault properties rather than dynamical stress fluctuations produced during earthquakes. Citation: Schmittbuhl, J., G. Chambon, A. Hansen, and M. Bouchon (2006), Are stress distributions along faults the signature of asperity squeeze?, Geophys. Res. Lett., 33, L13307, doi:10.1029/2006GL025952.

Relative influence of mechanical and meteorological factors on avalanche release depth distributions: An application to French Alps

The evaluation of avalanche release depth distributions represents a challenging issue for the mapping, zoning and long-term hazard management in mountainous regions. To that aim, both the distribution of snowfalls and the occurrence probability of an avalanche release for a given snow height need to be assessed. In this study, a rigorous formalism allowing coupling of these two ingredients into a mechanical-statistical model is presented. The stability criterion of a layered snowpack is investigated using a finite-element analysis accounting for the spatial heterogeneity of weak-layer mechanical properties, while the available snow depth is evaluated by studying the distribution of 3-day extreme snowfalls. The release depth distributions predicted by this coupled model are then compared to a well- documented database encompassing 369 natural slab avalanches recorded in La Plagne, France. It appears that with only one adjustable parameter, an excellent agreement can be obtained both for the power-law tail of the distribution, corresponding to large slab depths, and for its core corresponding to shallow slab depths. Two important conclusions can be drawn: (1) Small to medium-sized avalanches are controlled mainly by mechanics, whereas large avalanches are influenced by a strong mechanical- meteorological coupling. (2) The release depth distributions, including the value of the power-law exponent obtained for large slab depths, are highly variable in space and cannot be regarded as universal. Finally, the model is extended using a robust interpolation procedure in order to produce maps of expected release depths for different return periods.

Gravitary Free Surface Flows Used as a Rheometrical Tool: The Case of Viscoplastic Fluids

We present experimental results concerning the behaviour of two viscoplastic fluids (Carbopol gel and kaolin slurry) in a free surface flow configuration. Our experiments are conducted in a 3 meter long and 0.4 meter wide inclined channel whose bottom consists of a conveyor belt moving upstream with a controlled velocity. At channel upper boundary, fluid recirculation is forced by a rigid wall perpendicular to the bottom. These specificities allow us to generate gravitary surges that are stationary in the laboratory frame. We compare the properties of these surges (height and non dimensional characteristic numbers) to predictions based on independent measurements of the fluid rheological parameters. Lastly, the perspectives offered by the conveyor belt channel to characterize the rheological behaviour of complex natural fluids, such as muddy debris flow matrix, are discussed.