Introduction to Seismic Anisotropy

Seismic anisotropy is a physical property of the Earth that describes the directional dependence of various seismic parameters, such as the velocity and attenuation of seismic waves. Today, it is generally accepted that some form of seismic anisotropy is present in the IC, in a similar way that it is in the Earth's crust and mantle, and in laboratory conditions under high temperatures and pressures, where it can be more directly examined.

Unsurprisingly, anisotropy is a widespread phenomenon encountered in nature and, therefore, in many fields of science andmeasurement techniques. For example, it occurs in the orientation of the magnetic field in plasmas, the growth of leaves, heat conduction, the random motion of water molecules in the brain, the formation of sediments, and the growth of crystals. We also encounter anisotropy across various branches of technology, such as spectroscopy, filtering, optics, sheet metal forming, and ultrasound imaging, among many other techniques.

The course of development of the IC anisotropy concept contains all elements normally present in a scientific process, where observations first lead to questions that then demand answers. The first and foremost question at the root of our fascination with IC anisotropy, “Is IC anisotropy the real mechanism behind seismological observations?”, is a driving force for a number of seismological studies. Another relevant question, “If there is IC anisotropy measurable by existing seismological techniques and spatial coverage, how widespread and large is it?”, naturally follows the first question. Consequently, many geoscientists wonder: “What is the physical mechanism behind IC anisotropy, and what can it tell us about the dynamics and history of our planet, how it formed, perhaps even how the geomagnetic field came to its existence and how it evolved?”