Translations:Dictionary:Anisotropy (seismic)/8/en

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  • At the scale of a single crystal (giga-Hertz frequencies), the small-scale structure is the arrangement of atomic cells.
  • At the scale of a core (mega-Hertz frequencies), the small-scale structure is the micro-geometry of the arrangement of grains and pores. In some rocks, the crystals are randomly oriented, so that although each is intrinsically anisotropic, the random averaging means that the rock itself is isotropic (this might describe some sandstones). In other rocks (e.g. shales), there is a preferred orientation of some crystals (e.g. clays, which often have the shapes of platelets, and commonly lie horizontally), usually established by the direction of gravity during sedimentation and lithification. (The complementary pore space, occupied by fluid or kerogen, is then also flat-lying.) By itself, this usually leads to polar anisotropy.