Translations:Migration - book/6/en

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An anticline is a ridge-shaped fold of stratified rock in which the strata slope downward from the crest. Some of the great oil fields of the world are located in very gentle anticlines, so to a good degree of approximation, the rock layers can be considered essentially flat and horizontal. The configuration of flat horizontal layers is known as the layer-cake model of stratigraphy, the simplest type of stratigraphy encountered in oil exploration. Because the reflecting interfaces are horizontal (or nearly so), waves going straight down will be reflected nearly straight up. Thus, wave motion will be essentially vertical. If the time axes on the records are placed in the vertical position, time will appear in the same direction as the raypaths. By using the correct wave velocity, the time axis can be converted into the depth axis. The result is that the primary reflections show the locations of the reflecting interfaces. Thus, in areas that have nearly level reflecting horizons, the primary reflections as recorded essentially show the correct depth positions of the subsurface interfaces.