Classical Migration Velocity Analysis: The previous imaging methods can be described as estimating the earth model by predicting synthetic data that best explains the observed data in the data domain. In contrast, image-domain inversion finds the velocity model that best explains the observed migration section in the image domain. The observed migration image is obtained by migrating the recorded data using an assumed velocity model. Each iteration of image-domain inversion updates both the velocity model and the migration image. One of the advantages of image-domain inversion is that migration untangles crossing events in the data domain and focuses them to the vicinity of the reflecting boundary. Hence, the migration image should have a higher signal-to-noise ratio (S/N) than the original data for a reasonably accurate velocity model.
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This book describes the theory and practice of inverting seismic data for the subsurface rock properties of the earth. The primary application is for inverting reflection and/or transmission data from engineering or exploration surveys, but the methods described also can be used for earthquake studies. I have written this book with the hope that it will be largely comprehensible to scientists and advanced students in engineering, earth sciences, and physics. It is desirable that the reader has some familiarity with certain aspects of numerical computation, such as finite-difference solutions to partial differential equations, numerical linear algebra, and the basic physics of wave propagation (e.g., Snell’s law and ray tracing). For those not familiar with the terminology and methods of seismic exploration, a brief introduction is provided in the Appendix of Chapter 1. Computational labs are provided for most of the chapters, and some field data labs are given as well. Matlab and Fortran labs at the end of some chapters are used to deepen the reader’s understanding of the concepts and their implementation. Such exercises are introduced early and geophysical applications are presented in every chapter. For the non-geophysicist, geophysical concepts are introduced with intuitive arguments, and their description by rigorous theory is deferred to later chapters.