Reference Work Entry

Encyclopedia of Geomagnetism and Paleomagnetism

pp 146-149

D″, Anisotropy

  • Michael Kendall

Dynamic processes within the Earth can align minerals and inclusions. The resulting rock fabric leads to seismic anisotropy, which means that seismic velocity at a position varies as a function of the direction of wave propagation. In contrast, isotropy refers to the case where velocity is not directionally dependent. For reference, seismic heterogeneity (or inhomogeneity) refers to variation in velocity with position. Conventional seismic imaging techniques (e.g., travel‐time tomography) invert data for the isotropic velocity heterogeneity of the mantle, and as such offer insights into thermal and chemical structures. There are though a growing number of methods for estimating seismic anisotropy. As anisotropy results from deformation processes, such analyses offer added insight into the dynamical nature of the Earth. Although we are still in the early stages of mapping anisotropy, it appears that it is most pronounced in the boundary layers of the Earth, regions where deformation is ...

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