David Forel

Seismic Data Processing with Seismic Un*x

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); and Real 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.

Amplitude preservation equations for DMO

The scattering equation for a small volume in which density and bulk modulus are slightly different from the surrounding uniform medium is used to derive an amplitude transformation for dip moveout (DMO). The transformation is arranged so that when there is no change in density there is no change in amplitude with offset. Correspondingly, the gradient in amplitude indicates the degree of the change in density. By integrating the discontinuity over a plane the equations for the thin layer can be derived. The final result is that the amplitude of each trace can be scaled before DMO by a linear ramp proportional to t, and can be scaled after DMO and NM0 by a ramp proportional to ti”.

Comments on “Anonymous reviews”

I recently read four letters in Eos against anonymous reviews and zero letters for. I feel the need to add one to zero. When I started reviewing manuscripts, I had the ethical choice of whether or not to sign my name. After some thought, I decided I would not. Today, I feel the same for the same reason: I do not want people to think about who I am; I want them to think about what I write. R.E. Criss and A.M. Hofmeister would have me throw off my “cloak of secrecy—the costume of crooks.” Would seeing my face make my argument clearer or is it an excuse to judge the messenger?