Seismic anisotropy
From Wikipedia, the free encyclopedia
Seismic anisotropy is a term used in seismology to describe the directional dependence of seismic wavespeed in a medium (rock) within the Earth.
[edit] Crustal Anisotropy
In the Earth's crust, anisotropy may be caused by aligned microcracks, shear fabric, layered bedding in sedimentary formations, or highly foliated rocks. Crustal anisotropy resulting from aligned cracks can be used to determine the state of stress in the crust. In most cases, cracks preferentially aligned with the direction of maximum compressive stress. In active tectonic areas, such as near faults and volcanoes, anisotropy can be used to look for changes in preferred orientation of cracks that may indicate a rotation of the stress field. Crustal anisotropy is very important in the production of oil reservoirs as fast directions can be synonymous with fluid flow directions.
[edit] Mantle anisotropy
In the mantle, anisotropy is normally associated with crystals aligned with the mantle flow direction. Due to their elongate crystalline structure, olivene crystals tend to align with the flow due to mantle convection. Anisotropy has long been used to argue whether plate tectonics is driven from below by mantle convection or from above by the plates, i.e. slab pull and ridge push.
