Shear-wave singularities of wave propagation in anisotropic media
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Vols. 1-18 (1924-1944), ISSN 0044-2801
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Abstract
Shear-wave singularities in systems of anisotropic symmetry are comparatively well known, but it has not been generally realised that they may cause anomalies in shear-wave propagation for neighbouring directions due to the behaviour of the polarizations. Singularities are places where the two shear-wave slowness surfaces are continuous with each other through common points. The most frequent type, a point singularity, is a place where the two surfaces are continuous with each other through the vertices of cone-shaped projections from the surfaces. For directions of propagation in a plane, which cuts the slowness surfaces near a singularity, the velocities of the two shear-waves approach each other in a pinch and at the pinch exchange polarizations and velocity gradients. These singularities do not cause anomalies in plane waves propagating in a uniform medium, but may cause mode conversion and pulse-shape modification to waves with spherical wave-fronts, and to rays of shear-waves, in varying anisotropic media.
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References
Crampin, S. (1977) A review of the effects of anisotropic layering on the propagation of seismic waves. Geophys. J. R. Astron. Soc. 49:9-27
Crampin, S. (1978) Seismic-wave propagation through a cracked solid: polarization as a possible dilatancy diagnostic. Geophys. J. R. Astron. Soc. 53:467-496
Crampin, S., Evans, J.R., Ucer, B., Doyle, M., Davis, J.P., Yegorkina, G.V., Miller, A. (1980a) Observations of dilatancy-induced polarizationanomalies and earthquake prediction. Nature 286:874-877
Crampin, S., Kirkwood, S.C. (1981) Velocity variations in systems of anisotropic symmetry. J. Geophys. 49:35-42
Crampin, S., McGonigle, R., Bamford, D. (1980b) Estimating crack parameters from observations of P-wave velocity-anisotropy. Geophysics 45:345-360
Crampin, S., Taylor, D.B. (1971) The propagation of surface waves in anisotropic media. Geophys. J. R. Astron. Soc. 25:71-87
Duff, G.F.D. (1960) The Cauchy problem for elastic waves in an anisotropic medium. Philos. Trans. R. Soc. Ser. A: 252:249-273
Synge, J.L. (1957) Elastic waves in anisotropic media. J. Math. Phys. 35:323-334