HR: 0830h
AN: S11C-0293    [PDF]
TI: Intrinsic Anisotropy of Textured Rocks
AU: * Cholach, P Y
EM: pcholach@phys.ualberta.ca
AF: Institute for Geophysical research, Department of Physics, University of Alberta, Edmonton, AB T6E 2J1 Canada
AU: Schmitt, D R
EM: doug@phys.ualberta.ca
AF: Institute for Geophysical research, Department of Physics, University of Alberta, Edmonton, AB T6E 2J1 Canada
AB: The seismic anisotropy of crustal terrains has been detected in numerous passive and active source seismic experiments and confirmed by the ultrasonic laboratory measurements on textured samples of the metamorphosed rock formations. This observed anisotropy might be produced by variety of causes, including developed texture (lattice preferred orientation (LPO) of constituent minerals), structural layering and aligned fracturing of the formations of interest. In the case of the deformed metamorphic rocks with highly developed texture, LPO is generally accepted to be the main cause of anisotropy and this type of anisotropy is called here intrinsic anisotropy. Forward modelling of the intrinsic anisotropy is based on the theory of elasticity of polycrystalline aggregates and takes into account information about the texture of the rock and elasticity of constituent minerals. Elastic constants of a textured mica aggregate, which is one of the sources of anisotropy in metamorphosed rocks, were calculated on the basis of the widely used Voigt, Reuss and Hill assumptions. Taking into account significant anisotropy of the single mica mineral and the consequent wide separation of the Voigt and Reuss (upper and lower) bounds of some of the elastic constants of the anisotropic aggregate, the Geometric mean method was employed to further refine the elasticity. The Geometric mean method is based on simple and physically meaningful assumption of the invertibility of the elastic constants into the elastic compliances and yields unique set of elastic constants that are independent of the averaging domain and usually lie within the Voigt-Reuss bounds. Limits of the seismic anisotropy of the mica aggregate have been estimated. Intrinsic anisotropy depends primarily on the level of anisotropy of constituent minerals and their alignment (strength of texture). Similar technique could be applied to investigate elasticity of multiphase polycrystalline aggregates as more realistic model for anisotropic metamorphic rocks.
DE: 3909 Elasticity and anelasticity
DE: 5102 Acoustic properties
DE: 7218 Lithosphere and upper mantle
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting