| dc.description.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, nonuniform,
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 constants c = c + δc that 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. | |
