Lesson No. 40: Linear Distribution of Velocity—IV. The Refraction Problem
Published:January 01, 1959
In a seismic exploration program, the problem of converting travel-times to subsurface depths is of fundamental importance. The necessary computational procedures for this conversion are considerably simplified if the assumption of a linear distribution of velocity with depth can be used. Consequently, one of the first problems to be solved in such a program is to determine whether an assumption of this type should be adopted; and, if so, what values of Vo and a are to be used.
Whether or not the hypothesis of a linear variation of velocity with depth may be a good approximation to the actual situation in any region can often be surmised from the lithology. One of the first items on the agenda of a seismic crew should be the “shooting” of a sufficient number of refraction profiles, laid out as ideally as possible on a flat surface and, it is hoped, over a “normal” subsurface.* This latter requirement can be attained by laying out a number of profiles. If the time-distance curves Ior two or more profiles in the area are substantially alike, the conclusion that the subsurface sections are “normal” and “flat” is almost certain to be a valid one.
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Lessons in Seismic Computing
“An elementary text and problem book containing 44 lessons in seismology arranged for selection or combination to cover the normal 36-week course, or for condensation into an 18-week course. The lessons begin without assuming more than secondary school mathematics. An elementary knowledge of calculus is desirable, though not required, for the last half of the book.”