WAVE-FRONTS IN DISSIPATIVE ANISOTROPIC MEDIA

The purpose of this work is to draw attention to several differences b etween wave propagation in dissipative anisotropic media and purely el astic anisotropic media. In an elastic medium, the wavefront is define d as the envelope of the family of planes that makes the phase of the plane waves zero. It turns out that this definition coincides with the wavefronts obtained from the group and energy velocities, i.e., the t hree concepts are equivalent. However, for plane waves traveling in di ssipative anisotropic media these concepts are different. Despite thes e differences, the velocity of the envelope of plane waves closely app roximates the energy velocity, and therefore can represent the wavefro nt from a practical point of view. On the other hand, the group veloci ty describes the wavefront only when the attenuation is relatively low , i.e., for Q values higher than 100. The values of the different velo cities and the shape of the wavefront are considerably influenced by t he relative values of the attenuation along the principal axes of the anisotropic medium. This means that the anisotropic coefficients in at tenuating anisotropic media may differ substantially from the correspo nding elastic coefficients. Moreover, it is shown that the usual ortho gonality properties between the slowness surface and energy velocity v ector and the wavefront and wavenumber vector does not hold for dissip ative anisotropic media.