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Next: Acknowledgment Up: Wave-equation migration velocity analysis Previous: WEMVA cost

Conclusions

I present a migration velocity analysis method using wavefield-extrapolation techniques that can address the challenges posed by velocity estimation in complicated media with sharp contrasts and fine-scale features. This method is formulated in the migrated image space, with an objective function aimed at improving the image quality. The method is based on a linearization of the downward continuation operator that relates perturbations of slowness models to perturbations of migrated images. Since the method is based on finite-difference extrapolation of band-limited waves, it naturally takes into account the multipathing that characterizes wave propagation in complex environments with large and sharp velocity contrasts. It also takes into account the full wavefield information, and not only selectively picked traveltimes, as it is currently done in state-of-the-art traveltime tomography.

I use prestack Stolt residual migration (storm) to define image perturbations by maximizing focusing and flatness of angle-domain common image gathers (adcig). In general, the image perturbations computed with this method can be too different from the background image, and we are in danger of subtracting images that are not in phase, violating the first-order Born approximation assumption. I avoid divergence of the inversion procedure when the velocity perturbations are too large, by not inverting directly the image perturbations obtained by residual migration, but by inverting linearized versions of them. Thus, I achieve a method which is robust with respect to large model perturbations, a crucial step for a practical MVA method.


next up previous print clean
Next: Acknowledgment Up: Wave-equation migration velocity analysis Previous: WEMVA cost
Stanford Exploration Project
11/4/2004