HR: 17:30h
AN: T52F-07    [PDF]
TI: Composite Anisotropies Revealed by P-Wave Velocity Data Under the Approximation of 2nd Rank Tensor
AU: * Louis, L
EM: laurent.louis@geol.u-cergy.fr
AF: UMR CNRS 7072 Univ. Cergy-Pontoise, Av.du Parc - Le Campus - Bat I, Cergy-Pontoise, 95031 France
AU: David, C
AF: UMR CNRS 7072 Univ. Cergy-Pontoise, Av.du Parc - Le Campus - Bat I, Cergy-Pontoise, 95031 France
AU: Robion, P
EM: philippe.robion@geol.u-cergy.fr
AF: UMR CNRS 7072 Univ. Cergy-Pontoise, Av.du Parc - Le Campus - Bat I, Cergy-Pontoise, 95031 France
AB: From diagenesis to tectonic stress induced deformation, rock microstructures always present some anisotropy associated with a preferential orientation, shape or spatial arrangement of its constituents. Considering the consequences this anisotropy has on directional transport and mechanical properties, as the geological history it carries, its 3D characterisation has received a particular attention in numerous works. A fast and simple way to give an overall estimation of the microstructural state of a rock sample is the determination of some physical property fabrics, provided that one is able to assign the measured anisotropies to one or more microstructural features. In non porous metamorphic and igneous rocks that often present a strong textural anisotropy, the relations between shape or lattice preferred orientation and acoustic or magnetic properties are quite well established. However, this is not the case for weakly anisotropic granular media in which the recognition of a microstructural anisotropy implies a statistical analysis on thin sections. In this latter case, anisotropy of magnetic susceptibility (AMS) has been intensively used in structural studies, providing a mid-scale (cm) tool to infer different stages of deformation depending on the position in the studied structure, but leading to an unresolved interpretation problem in terms of microstructures since the origin of the magnetic signal rarely fits a directly observable feature. In the work that will be presented, we propose to complete the classical AMS approach with the estimation of P-wave velocity anisotropies (APV), assuming that this property, like the magnetic susceptibility, supports also a tensorial notation as a first order approximation. Through a careful study of samples retrieved from different deformed structures, we show that P-wave velocities reveal a strong sensitivity to all observable anisotropic microstructural features, which is used to highlight evidences for location-dependence of grain-scale fabrics.
DE: 5102 Acoustic properties
DE: 5112 Microstructure
DE: 8005 Folds and folding
SC: Tectonophysics [T]
MN: 2003 Fall Meeting