Diving waves in acoustic factorized orthorhombic media

Abstract

Diving waves propagating in the subsurface are massive sources of low-frequency information that can be used to constrain the kinematic component of the velocity model. Compared to reflected waves, less is known about the behaviour of diving waves, especially in the presence of azimuthal anisotropy. Anisotropy is needed to place the events to the correct depths and match travel times in synthetics with recorded data. Obtaining more insights into the influence of anisotropy on diving wave propagation can help to find parameters with a low trade-off for inversion. Here, we derive equations for diving qP-waves in an acoustic factorized anisotropic model with orthorhombic anisotropy. The effects of the anisotropic parameters in the acoustic factorized orthorhombic model are tested by perturbing ${\epsilon }_1$, ${\epsilon }_2$, ${\eta }_1$, ${\eta }_2$ and ${\eta }_3$ and observing differences in the ray paths, the effective vertical slowness and the relative geometrical spreading. The properties of diving waves in this model are also compared with those in an acoustic isotropic model and acoustic factorized anisotropic models with elliptical- and vertical transverse isotropic anisotropy. From our analysis, we found that perturbing ${\epsilon }_1$ and ${\epsilon }_2$ has the most significant influence on these characteristics. The ${\eta }_1$, ${\eta }_2$ and ${\eta }_3$ parameters were shown to induce minor changes. Compared with the other models, the acoustic factorized orthorhombic model had the most in common with the acoustic factorized anisotropic model with elliptical anisotropy. Although, in general, none of the other models could fully represent the effects of orthorhombic anisotropy.