A Crackling Crust (une croute craquante)
Monday, March 18, 2002 - 9:10am - 10:10am
Yves Gueguen (École Normale Supérieure)
Fractures in the crust cover a broad range of scales, from microcracks to large fractures. They control both transport and mechanical properties of rocks, which are of major importance in geology and geophysics. An attempt to clarify our understanding of these properties will be presented as follows. At small scales, the homogeneity of the medium is in general sufficient to assume statistical homogeneity (or equivalently Translational Invariance). Effective Medium Theory allows in that case to derive elastic properties and permeability. As the scale increases however, heterogeneity increases also, so that the assumption of Translational Invariance breaks down, clustering effects are important, and critical thresholds are observed. The assumption of Scale Invariance may be more relevant in such situations than that of Translational Invariance, and various methods inspired from percolation theory can be useful. Elastic wave velocities and permeability of rocks will be discussed using these concepts, and strain localization as well. It will be argued that these physical approaches provide a powerful framework to interpret geophysical data on a sound basis.