This volume, SEG Course Notes Series No. 13, is designed to give the practicing geophysicist an understanding of the principles of poststack migration, presented with intuitive reasoning rather than laborious math. Modeling is introduced as a natural process that starts with a geologic model and then builds seismic data. Migration is then described as the reverse process that uses seismic data to find the geologic model. Many other topics are covered relating to the quality of the migrated section, such as aliasing, rugged topography, or use of the correct velocity. Significant new material has been added in this revised edition of the original 1997 book, especially algorithms based on the phase-shift method, such as PSPI and the omegaX method.

Our objective is to introduce you to the fundamentals of seismic data processing with a learn-by-doing approach. We do this with Seismic Un*x (SU), a free software package maintained and distributed by the Center for Wave Phenomena (CWP) at the Colorado School of Mines (CSM). At the outset, we want to express our gratitude to John Stockwell of the CWP for his expert counsel.SU runs on several operating systems, including Unix, Microsoft Windows, and Apple Macintosh. However, we discuss SU only on Unix. Detailed discussion of wave propagation, convolution, cross- and auto-correlation, Fourier transforms, semblance, and migration are too advanced for this Primer. Instead, we suggest you refer to other publications of the Society of Exploration Geophysicists, such as “Digital Processing of Geophysical Data – A Review” by Roy O. Lindseth and one of the two books by Ozdogan Yilmaz: “Seismic Data Processing,” 1987 and “Seismic Data Analysis,” 2001.Our goal is to give you the experience and tools to continue exploring the concepts of seismic data processing on your own.This Primer covers all processing steps necessary to produce a time migrated section from a 2-D seismic line. We use three sources of input data:Synthetic data generated by SU;Real shot gathers from the Oz Yilmaz collection at the Colorado School of Mines (ftp://ftp.cwp.mines.edu/pub/data); andReal 2-D marine lines provided courtesy of Prof. Greg Moore of the University of Hawaii: the “Nankai” data set and the “Taiwan” data set.The University of Texas, the University of Tulsa, and the University of Tokyo collected the Nankai data. The U.S. National Science Foundation and the government of Japan funded acquisition of the Nankai data.The University of Hawaii, San Jose State University, and National Taiwan University collected the Taiwan data. The U.S. National Science Foundation and the National Science Council of Taiwan funded acquisition of the Taiwan data.Chapters 1–3 introduce the Unix system and Seismic Un*x.Chapters 4–5 build three simple models (complexity slowly increases) and acquire a 2-D line over each model. (These chapters may be skipped if you are only interested in processing.)Chapters 6–9 build a model based on the previous three, acquire a 2-D line over that model, and process the line through migration.Chapters 10–11 start with a real 2-D seismic line of shot gathers (Nankai) and process it through migration.Chapters 12–13 and 15–16 start with a real 2-D line of shot gathers (Taiwan) and process it through migration.

This document can either be printed or followed as an Adobe Acrobat PDF file (included on the CD-ROM). As a PDF file, each item on the Contents page is linked to its corresponding location, and the user can return to Contents by clicking the Page Number at the bottomcenter of every page. Additionally, all references in this tutorial are linked to the appropriate location in Appendix A (the Reference list).The main portion of this tutorial is Section 2, Processing Steps and Associated Pitfalls, which focuses on individual processing procedures, each of which is broken into three parts:The basics of the process are discussed briefly with graphical examples when appropriate.The procedure is applied to the Kansas or England example data with emphasis on the most important parameters.The procedure is applied to the Kansas or England example data with emphasis on the most important parameters.The seismic data examples in this Primer were processed and displayed using Seismic Processing Workshop (Parallel Geoscience Corporation) on a Macintosh G3 computer.The first published examples of seismic reflections detected shallower than 50 m are from Pakiser and others at the U.S. Geological Survey (Pakiser and Mabey, 1954; Pakiser et al., 1954; Pakiser and Warrick, 1956; Warrick and Winslow, 1960). Digital seismographs were not yet available, and the method was not strongly pursued until the late 1970s and early 1980s. A classic paper by Hunter et al. (1984) developed the optimum-window technique, first used for constant-offset surveying but now adopted in typical common-midpoint (CMP) processing.

In this chapter the benefits of depth imaging are reviewed. The distinction between depth conversion through depth imaging and map-based depth conversion is made. The four principle geophysical advantages are defined. Traditional barriers to depth imaging are described.Figure 1.1 is a flow chart which makes the distinction between traditional map-based depth conversion and image-based depth conversion. Both procedures begin with CMP gathers and end with depth maps. Map-based depth conversion relies on time imaging to define the structural framework. Velocity variation is expressed in the form of layer interval velocity maps, and time-depth conversion is performed through grid operations. In contrast, image-based depth conversion utilizes depth imaging to define the structural framework. The depth conversion is part of the imaging process and velocity information is obtained in the imaging process itself.The key difference between the techniques is first, in image-based depth conversion, the structural interpretation is made utilizing the superior imaging capability of depth imaging, and second, that depth imaging is, in itself, a strong velocity estimation tool.Before reviewing the geophysical basis for the expectation that depth images will be superior it is worth examining some data examples that show, from a geologic standpoint, the additional structural information gained. Figures 1.2 to 1:12 are time and depth image comparisons from a variety of structural settings.Salt examples - Figure 1.2 is from a salt sill in the deepwater Gulf of Mexico. The time image shows a complex arrangement of reflectors in the subsalt section. In the depth image the subsalt section is shown to be planar and relatively unbroken (there remains a single shadow zone below the nose of the sill) with a slight dip away from the salt sill. The base of salt reflections show alternations of steep and moderate dip perhaps related to changes in sedimentation rate versus speed of salt sill advancement. The development of this depth image is reviewed in the case history by Egozi in this volume.Figure 1.3 depicts a salt diapir from the transition zone of the Gulf Coast. Exploration in this area often relies on an accurate estimate of the position of the salt sediment interface. Where the diapir flank becomes steep the time image shows little information. The depth image renders the interface continuously; where it is vertical and even where it is overhung.Figure 1.4 depicts a salt-cored anticline in the Southern North Sea. The high amplitude reflection near the base of the time image is a salt weld along which the upper Permian salt has been evacuated.

“Seismic modeling and imaging of the earth's subsurface are complex and difficult computational tasks. The authors present general numerical methods based on the complete wave equation for solving these important seismic exploration problems.”

“This publication is designed to provide a practical understanding of leastsquares methods of parameter estimation and uncertainty analysis. The practical problems covered range from simple processing of time- and space-series data to inversion of potential field, seismic, electrical, and electromagnetic data. The various formulations are reconciled with field data in the numerous examples provided in the book; well-documented computer programs are also given to show how easy it is to implement inversion algorithms.”

“Synergisms among tectonics, sedimentation, and climate/sealevel oscillations provide hydrocarbon source, reservoirs, and traps. This book from the SEG Course Notes series examines these traits, as they exist in the on- and offshore region of Louisiana.”

“This volume assists geophysicists in implementing and evaluating DMO processing. It discusses the theory, motives, and limitations underlying the most popular DMO methods.”