Seismic anisotropy

Summary

Seismic anisotropy is the dependence of seismic wave speeds on the direction of propagation and on the direction of polarization. It is the seismological side of anisotropic elasticity: the speeds come from the Christoffel equation for the elastic stiffness tensor of the rock. It arises from aligned crystals, such as olivine in the upper mantle, from fine layering, and from aligned cracks. Measuring it reveals the direction of past and present deformation and flow inside the Earth.