Isotropic angle-domain elastic reverse-time migration

Conclusions

We present a method for reverse-time migration with angle-domain imaging formulated for multicomponent elastic data. The method is based on the separation of elastic wavefields reconstructed in the subsurface into pure wave-modes using conventional Helmholtz decomposition. Elastic wavefields from the source and receivers are separated into pure compressional and transverse wave-modes which are then used for angle-domain imaging. The images formed using this procedure are interpretable in terms of the subsurface physical properties, for example, by analyzing the PP or PS angle-dependent reflectivity. In contrast, images formed by simple cross-correlation of Cartesian components of reconstructed elastic wavefields mix contributions from P and S reflections and are harder to interpret. Artifacts caused by back-propagating the recorded data with displacement sources are present in both types of images, although they are easier to distinguish and attenuate on the images constructed with pure elastic wave-modes separated prior to imaging.

The methodology is advantageous not only because it forms images with clearer physical meaning, but also because it is based on more accurate physics of wave propagation in elastic materials. For example, this methodology allows for wave-mode conversions in the process of wavefield reconstruction. This is in contrast with alternative methods for multicomponent imaging which separate wave-modes on the surface and then image those independently. In addition, elastic images can be formed in the angle-domain using extended imaging conditions, which offers the potential for migration velocity analysis (MVA) and amplitude versus angle (AVA) analysis.

Isotropic angle-domain elastic reverse-time migration