Geological significance of anisotropy of seismic velocities in Earth's crust

Anisotropism of seismic velocities is at its minimum in rocks consisting mainly of feldspar and quartz, is appreciable in pyroxenes and amphiboles (chain-structured silicates), and is at its maximum in mica-rich rocks (sheef-structured silicates). Inasmuch as the difference between the formation and boundary velocities has been established by the DSS for the Earth's crust, as a whole, and is recognizable also in the tops of the mantle, the crust and the tops of the mantle probably consist of seismically anistropic rocks. -- IGR Staff.