The sonic log is fundamental to the reflection seismologist because it represents the relation between the seismic reflection response recorded at the earth's surface and subsurface stratigraphy. Explorationists should be familiar with the development of sonic-logging tools and the accuracy with which the interval velocity can be obtained from each generation of tool development. Current tools, such as the long-spacing sonic log and the digitized sonic wave-form log, hold great promise in providing the quality of interval velocity data explorationists have long desired.

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