Anisotropy surface waves

Fig. 11.4. Velocities of bulk and surface waves in an (001) plane the angle of propagation in the plane is relative to a [100] direction, (a) Zirconia, anisotropy factor Aan = 0.36 (b) gallium arsenide, anisotropy factor Aan = 1.83 material constants taken from Table 11.3. Bulk polarizations L, longitudinal SV, shear vertical, polarized normal to the (001) plane SH, shear horizontal, polarized in the (001) plane. Surface modes R, Rayleigh, slower than any bulk wave in that propagation direction PS, pseudo-surface wave, faster than one polarization of bulk shear wave propagating in...

Surface waves also provide a means for estimating upper-mantle anisotropy. There are three canonical ways of detecting anisotropy using surface waves. One comes from discrepancies in isotropic inversions of Love and Rayleigh phase velocities (e.g. Anderson 1961) and leads to transversely isotropic models or polar anisotropy. Another comes from azimuthal variations in phase velocities (e.g. Forsyth 1975) and leads to models of azimuthal or radial anisotropy. 

We see evidence for velocity structure and anisotropy within the tectosphere. Surface waves reveal evidence for a thin high-velocity layer, 5-20 km thick, which lies beneath a 37-43 km thick crust. Wide-angle refractions also show these features (Kay et al. 1999a Musacchio et al. 

Inversions of body wave arrival times for three-dimensional velocity structures are common practice at volcanoes using teleseismic waves, local earthquake sources, and active seismic sources. These inversions can also account for 3D Vp azimuthal anisotropy, which is parameterized with a percent anisotropy and an orientation of the fast axis. Seismic anisotropy can be detected using inversions of Love and Rayleigh surface waves from large earthquakes in the same manner. 

Surface waves constructed from cross-correlations of ambient seismic noise can be inverted for 3D seismic velocity structure. Seismic anisotropy from ambient noise tomography can be calculated. These calculatimis are different from the time-lapse studies that detect temporal variations in isotropic seismic velocities using ambient noise interferometry (see Tracking Changes in Volcanic Systems with Seismic Interferometry ). 

Fig. 11.5. Profile of the particle displacement velocities in a Rayleigh wave in a GaAs(OOl) surface, propagating at an angle = 15° to a [100] direction. This figure is analogous to Fig. 6.2(b) for a Rayleigh wave in an isotropic medium, but in this case there are components of displacement in both horizontal axes, because of the anisotropy, and so three curves are needed they are normalized by setting the larger horizontal component to unity at the surface.

The mean diffusion length of the minorities is drastically dependent on crystal imperfections. It may also be dependent on surface orientation, if they have an anisotropic mobility. Optical anisotropy is necessary for seeing an influence of crystal orientation on the penetration depth of the light while crystal imperfections will only affect the penetration depth in a range of wave lengths where light absorption in the crystal is very weak. The photocurrents are very small in this case which will not be discussed here. 

The photo-dissociation dynamics at 193 nm was analyzed in detail and the observed rotational state distribution was obtained by using the rotation reflection principle by Schinke and Stasemler [53]. All rotational state distributions depend sensitively on the anisotropy of the dissociative potential energy surface. These are interpreted as a mapping of the bound state wave function onto the quantum number axis. The mapping is mediated by the classical excitation function determined by running classical trajectories onto the potential energy surface within the dissociative state. This so-called rotation-reflection principle... 

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