This presentation will encompass the material of our 2005 convention paper of the same name but with more background. I will discuss the general concept of seismic depth migration by downward continuation using wavefield extrapolation. Wavefield extrapolation imaging (also known as wave-equation migration) has theoretical advantages over the more widely used Kirchhoff method but faces a number of technical challenges, one of which is operator stability. Following this general, conceptual overview, I will present our new approach to the design of stable and accurate wavefield extrapolation operators. We split the theoretical operator into two component operators, one a forward operator that controls the phase accuracy and the other an inverse operator, designed as a Wiener filter, that stabilizes the first operator. Both component operators are designed to have a specific fixed length and the final operator is formed as the convolution of the components. We utilize this operator design method to build an explicit, wavefield extrapolation method based on the migration of individual source records. Two other features of our method are the use of dual operator tables, with high and low levels of evanescent filtering, and frequency-dependent spatial down sampling. Both of these features improve the accuracy and efficiency of the overall method. I illustrate the method with tests on the Marmousi synthetic dataset. We call our method FOCI which is an acronym for forward operator conjugate inverse.
The complete article on this topic may be found in the September’ 2005 issue of the RECORDER.
About the Author(s)
Gary Margrave is Associate Professor of Geophysics and Mathematics at the University of Calgary. He is also Associate Director of CREWES and the U of C Site Director for PIMS. Before joining the University of Calgary in 1995, he spent fifteen years with Chevron Corporation where he held a variety of geophysical positions. He obtained his Ph.D. in geophysics from the University of Alberta in 1981. Dr. Margrave’s expertise is in the research, teaching and application of exploration seismology, including seismic data processing, migration and mathematical signal theory. His research interests include signal band estimation, seismic attenuation, deconvolution, imaging and seismic wave propagation.