Translations:Wave velocity/7/en

Several features make rocks anisotropic. Anisotropy causes the average elastic constants to depend on direction. A common type of anisotropy is the result of fine layering. For example, the Austin Chalk has alternating hard and soft layers, each of which is only a few centimeters thick. For low-frequency seismic waves, the Austin Chalk can be described as a homogeneous but anisotropic medium. Its average properties depend on the contrast between layers. Another source of anisotropy is block fracturing. Such fracturing results from past episodes of tectonic movement. A third source of anisotropy is caused by unequal stress fields existing in the rock.