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Full waveform inversion using simultaneous encoded sources based on first- and second-order optimization methods Open Access


Other title
Full waveform inversion, wave-equation, simultaneous sources, inversion, optimization
Type of item
Degree grantor
University of Alberta
Author or creator
Anagaw, Amsalu Y.
Supervisor and department
Sacchi, Mauricio D. (Physics, University of Alberta)
Examining committee member and department
Gu , Yu J. (Physics, University of Alberta)
Innanen , Kristopher A. (Geoscience, University of Calgary)
Schmitt, Douglas R. (Physics, University of Alberta)
Sydora, Richard (Physics, University of Alberta)
Minev, Peter D. (Mathematics, University of Alberta)
Department of Physics
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Full waveform inversion (FWI) is an emerging seismic technology engine for estimating subsurface model parameters such as velocity, density and attenuation through local minimization of an objective function. The minimization problem is often performed iteratively via gradient-based method that is based on the first-order derivatives of the objective function. One of the major obstacles of FWI that hinders its practical applications for estimating subsurface model parameters for large scale problems is its huge computational demand for performing many forward modeling for multiple sources. One way to reduce the overall cost of waveform inversion is by adopting a simultaneous source strategy. In other words, multiple sources are simultaneously fired to simulate super-shot gathers and thereby reduce the number of seismic modeling simulations that are performed during the inversion. However, the use of simultaneous sources introduces cross-talk artifacts that arise from the interference among the sources that constitute a super-shot. In this thesis, we study and extend the practical applications of the second-order optimization methods in the framework of simultaneous sources. First, we examined the effect of model parameterizations on velocity model building using Newton-based optimization methods. Three model parameterizations for the acoustic FWI were investigated. These include velocity, slowness and slowness squared. We then analyze the influence of different simultaneous multi-frequency selection strategies on cross-talk artifacts. Our analysis focuses on a multiscale frequency-domain FWI algorithm that is implemented with simultaneous sources that are randomly encoded with a source-encoding function. In the multiscale conventional FWI inversion strategies, a finite set of discrete frequencies will be selected and the inversion is carried out sequentially from low to high frequency data components. We examine six frequency selection strategies and test the performance of the algorithm with encoded datasets. Numerical tests show that high fidelity results can be attained by inverting partially overlapped groups of temporal frequencies. In order to mitigate cross-talk artifacts during the numerical inversion, a new encoding is generated at every iteration. We also found that high resolution images can be obtained by re-sampling new source positions and new encoding functions at every iteration of the FWI algorithm. Finally, we present a full Newton FWI algorithm and its application in the presence of high amplitude multi-reflected waves that are generated by strong velocity contrast and/or from free surface reflections.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Anagaw, A. and M. Sacchi. “Comparison of multifrequency selection strategies for simultaneous-source full-waveform inversion.” Geophysics 79 (2014): R165–R181.Anagaw, A. and M. Sacchi. “Regularized 2D Acoustic Full Waveform Inversion.” 73rd EAGE Conference & Exhibition, EAGE Expanded Abstracts (2011): P027.Anagaw, A. and M. Sacchi. “Full waveform inversion with simultaneous sources using the full Newton Method.” SEG Technical Program Expanded Abstracts 531 (2012): 1–5.

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