Abstract
The time hierarchy of seismograms recorded on the Earth makes the ray theory an exceptional modeling and interpretative tool for understanding how waves propagate inside the Earth. Basic ingredients of such theory as well as necessary extensions required by the failure of the ray ansatz are introduced. Different techniques for ray tracing are discussed with specific advantages, making the choice of the most suitable tool problem dependent. Both traveltime and amplitude estimations are described through kinematic and dynamic (also known as paraxial) formulations. Theories such as WKBJ, Maslov, or Gaussian Beam summations are presented before coherent-state transformation approach. The geometrical theory of diffraction is summarized because of the vast literature on such a difficult subject. The influence of finite frequency contents with the concept of Fresnel volumes is addressed before considering single diffraction approaches as Ray+Born/Rytov or Ray+Kirchhoff formulations. Finally, the concept of ray theory appears very modern and particularly adapted to the investigation of the Earth’s interior. Understanding ray theory remains a key tool for mastering body-wave propagation in the Earth.
Published Version
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