Seismic ray theory

Summary

Seismic ray theory is the high-frequency approximation of elastic wave propagation in which energy travels along curves called rays. The travel time solves an eikonal equation, and the rays obey Fermat's principle, as light rays do in geometric optics. It is the basis of earthquake location, travel-time tables and travel-time tomography. It is accurate when the wavelength is much shorter than the scale on which the medium changes.