title: Propagation of elastic waves through textured polycrystals: application to ice.
abstract: The propagation of elastic waves in polycrystals is revisited, with an emphasis on configurations relevant to the study of ice. Randomly oriented hexagonal single crystals are considered with specific, non-uniform, probability distributions for their major axis. Three typical textures or fabrics (i.e. preferred grain orientations) are studied in detail: one cluster fabric and two girdle fabrics, as found in ice recovered from deep ice cores. After computing the averaged elasticity tensor for the considered textures, wave propagation is studied using a wave equation with elastic constantsc=〈c〉+δcthat are equal to an average plus deviations, presumed small, from that average. This allows for the use of the Voigt average in the wave equation, and velocities are obtained solving the appropriate Christoffel equation. The velocity for vertical propagation, as appropriate to interpret sonic logging measurements, is analysed in more details. Our formulae are shown to be accurate at the 0.5% level and they provide a rationale for previous empirical fits to wave propagation velocities with a quantitative agreement at the 0.07-0.7% level. We conclude that, within the formalism presented here, it is appropriate to use, with confidence, velocity measurements to characterize ice fabrics.
authors.affiliation: Institut Langevin, CNRS , ESPCI ParisTech , Paris 75005, France.
authors.forename: Agnès
authors.initials: A
authors.lastname: Maurel
authors.affiliation: Departamento de Física, Facultad de Ciencias Físicas y Matemáticas , Universidad de Chile , Casilla 487-3, Santiago, Chile.
authors.forename: Fernando
authors.initials: F
authors.lastname: Lund
authors.affiliation: LGGE, CNRS , Université de Grenoble Alpes , Grenoble 38041, France.
authors.forename: Maurine
authors.initials: M
authors.lastname: Montagnat
keywords: effective medium; elastic wave propagation; ice; polycrystal