(an, ī so’ tr∂p ē or a nī’ sō tr∂p ē) Variation of a physical property depending on the direction in which it is measured. Anisotropy involves directional variation at one point as opposed to heterogeneity, which involves variation from point to point. Both anisotropy and heterogeneity are matters of scale, and so their usage relates to the wavelengths involved.
Crystals exhibit intrinsic anisotropy and crystal nomenclature (based on symmetry systems, q.v.) is sometimes used to define the types of anisotropy. Plate-like mineral grains and interstices tend to orient themselves parallel to sediment bedding, producing granular anisotropy. Layering and oriented fractures also can produce anisotropy. Aeolotropy is also used.
- Thomsen, 2002, Understanding seismic anisotropy in exploration and exploitation: SEG-EAEG Distinguished Instructor Series #5: Soc. Expl. Geophys.