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Acoustic VTI Full-waveform Inversion with 3-D Free-surface Topography
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 79th EAGE Conference and Exhibition 2017, Jun 2017, Volume 2017, p.1 - 5
Abstract
In land applications, topography may impact the imaging if not taken into account. With low-frequency and wide-aperture data, the long-to-intermediate wavelength components of the velocity model can be recovered by full-waveform inversion. Standard static corrections to handle the topography do not work satisfactorily on long-offset data. We present a method to handle 3-D free-surface topography for acoustic FWI by directly modelling the effect of the topography with an immersed-boundary finite-difference scheme. The numerical scheme is aimed specifically at first-order wave equations discretized on standard staggered grids, using high-order derivative operators that are modified based on their relative position to the free surface. We extend the approach to VTI media to be able to model velocity anisotropy required in long-offset inversions. We then investigate the topography artefacts seen on real land full-waveform inversions in relatively simple synthetic experiments, allowing us to quantify the effect of elevation variation on the inversion accuracy. The experiments demonstrate that elevation variations in the order of 1/4 wavelength or somewhat smaller can already create artefacts in the inversion results if ignored.