Full Waveform Inversion of Crosshole Data in Tilted Transversely Isotropic Media

Abstract

Summary We apply the joint approach of traveltime tomography and Full Waveform Inversion (FWI) to a synthetic experiment in media exhibiting Tilted Transverse Isotropy (TTI) Symmetry. We adopt a Finite-Difference Frequency-Domain (FDFD) approach for modeling acoustic waves within the seismic modeling framework, Zephyr. The synthetic crosshole experiment consists of a tilted layer sequence chosen to simulate a realistic TTI environment. Models of seismic velocity and the anisotropic parameters were obtained from anisotropic traveltime inversion and used as the starting models for monoparameter FWI to update the velocity model only. The effects of parameter crosstalk are evident within the traveltime results and are mitigated by the application of a Gaussian smoothing operator before FWI. The final FWI model contains all of the prominent features from the true model, although there are some artefacts present in these results. Steeply dipping artefacts are introduced due to mismatches between the velocity and background anisotropy models at larger offsets. We mitigate the presence of these artefacts by stringent offset weighting of the data at lower frequencies. The successful application of FWI to this synthetic experiment suggests that this approach is a suitable candidate for field data which display TTI symmetry.