M.S. Howard, S.H. Danbom, 1983. "Random Noise Example", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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Figure 1 (left) is a common-shot-point gather of synthetically made seismic traces using a random number generator. These data would represent the zero end point of the signal-to-noise ratio spectrum -a ratio commonly used to measure the reflection signal strength as compared to random ambient noise. Figure 2 (center) is a final stacked section made from a collection of these random field files. The processing sequence that resulted in this figure is common to the industry (elevation static corrections, sort to common-depth-point gathers, normal velocity moveout corrections, etc.). These data will necessarily still be random, but an interpreter who is extremely hardened to working in poor record areas may see some chance alignments in this display. Perhaps this can be more clearly seen by viewing the section obliquely.
Figure 3 (right) results when these final stacked traces are mathematically manipulated by a new modern processing technique. In essence, this figure results when severe trace mixing is the end result of a process that is more sophisticated at face value. Here, the chance alignment is enhanced by the mixing process. Whereas this particular method would not be misused by the scrupulous processing geophysicist, Figure 3 should alert anyone who commonly works with seismic data in poor record areas to the possible dangers of signal enhancement beyond reasonable limits.
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Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces
Until a few decades ago, structural and regional geology were traditionally the preserve of field geologists. They usually mapped areas of outcropping deformed rocks and supplemented their work by laboratory studies of rock deformation and by theoretical work. Structural geology became tied to the geology of uplifts, folded belts, and underground mines, all of which were accessible to direct observation. Since World War II we have witnessed a tremendous development of geophysics in oceanography and in petroleum geology. Academic geophysicists in oceanography led their geological colleagues into modern plate tectonics and industry geophysicists developed reflection seismology into a superb structural mapping tool that penetrated the subsurface.
Today we are facing a situation where instruction and textbooks in structural geology are almost entirely dedicated to rock deformation, analytical techniques in detailed field geology and summaries of plate tectonics. Illustrations based on reflection seismic profiles are virtually absent in textbooks of structural geology. These texts illustrate only the parts of the proverbial elephant, together with some conjecture, but without ever offering a glimpse of the whole elephant.
Some of the reason cited for the relative scarcity of published reflection profiles are: 1) the confidentiality of exploration data; 2) difficulties in the photographic reduction and reproduction of seismic profiles for a book format; 3) the two-dimensional nature of vertical reflection profiles; and 4) the obvious distortions in reflection profiles that are typically recorded in time.
The AAPG leadership felt that it was time to attempt to correct the situation and to produce this picture and work atlas. The first volumes, of what may become a series of volumes, are addressing an audience that includes: petroleum geologists concerned with structural interpretations; exploration companies that provide in-house training; the AAPG continuing education program; and academic colleagues interested in updating their curricula in structural geology by inclusion of reflection profiles from the “real world” in their teaching.
The atlas is not meant to be a textbook in reflection seismology (instead we listed some at the end of this introduction) nor a text in structural and/or regional geology. Our intent is simply to provide a teaching tool.