Elastic Full Wavefield Migration using Shuey’s approximation

The phenomenon of wave conversions, where acoustic, pressure (P) waves are converted to elastic, shear (S) waves is commonly disregarded in seismic imaging, which can lead to lower-quality images in regions with strong reflectors. While a number of methods exist which do take wave conversions into account, most deal with P- and S-waves separately, rather than in using a single, unified, framework. Elastic Full-Waveform Inversion (FWI), on the other hand, which does offer a unified framework for all elastic effects, is prohibitively computationally expensive in many cases.

We present an alternative approach by extending Full Wavefield Migration (FWM) to account for wave conversions. Full Wavefield Migration describes seismic data in terms of convolutional propagation and reflection operators in the space-frequency domain. By applying these operators recursively, multi-scattering data can be modelled and inverted. Using Shuey’s approximation to constrain the number of parameters necessary to describe the full, elastic, reflection and transmission operators, we present an elastic FWM algorithm which accounts for wave conversions.

The resulting algorithm is tested on a synthetic model to give a proof of concept. The results show that the proposed extension can model wave conversions accurately and yields better inversion results than applying conventional, acoustic FWM.