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Structural geologists have made tremendous strides in unraveling the architecture of the earth with recent studies of seismic reflection data.
This is true not only for exploration studies, but also for crustal studies. However, the seismic time section is not an undistorted cross section of the earth.
Seismic sections across most geologic structures are distorted by sideswipe and/or lateral velocity changes in the subsurface. Invariably, the distortion on the 2-D migrated section hides the features that are most desired. However, through seismic models of similar geologic structures, the interpretational pitfalls caused by sideswipe and velocity are turned into practical prediction tools.
Migrated seismic lines across domes and anticlines normally exaggerate the size of the anomalies. Migrated seismic lines across synclines and basins are characterized with false expressions that include grabens, contemporaneous deformation, cross-stratification, high amplitudes, and crossing reflections. Geologic areas that have large lateral velocity contrasts, such as reefs, diapirs, or fault blocks, exhibit false seismic expressions. These include relief faults, basement-controlled tectonics, facies changes, and structures that are located in geologically ambiguous positions. Even the polarity of the seismic reflection is 3-D dependent.
Modeling examples show that interpretational pitfalls, such as mapping from migrated sections and interpreting from the basement upward, must be supplemented with pseudo-3-D interpretational techniques. Geologic models and their seismic analyses from salt provinces, reefs, overthrusts, etc, illustrate these pseudo-3-D interpretational tools.
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