A comment on the form of the geometrical spreading equations, with some numerical examples of seismic ray tracing in inhomogeneous, anisotropic media

Abstract

We point out that while the equations of seismic ray geometrical spreading given recently by Norris do differ as stated from equations given by Červený, it does not imply that the latter equations are wrong. The two sets of equations differ only in form and in a way which, in part at least, can be ascribed to different choices of Hamiltonian by the two authors. Quantitatively, though, the two sets of equations are entirely equivalent. We also present some numerical results of ray tracing in anisotropic models simulating a continential rift, a spreading ridge and a subduction zone. These three structures span a range of geological mechanisms for seismic anisotropy. Though definitive conclusions cannot be easily drawn when there is both anisotropy and inhomogeneity, the results do indicate the magnitude of ray path, travel-time and amplitude variations to be expected for P-waves when anisotropy is introduced.