The concept of "semblance" is a new likeness or coherency measure, and is related to energy-normalized cross correlation. All coherency measures must be considered from three basic viewpoints--the domain in which they are applied, the philosophy of their design, and their manner of use.

The most familiar of the likeness or coherency measures is cross correlation. Differences in design philosophy mainly involve changes in normalization. The "semblance" concept, thus, contains elements of both. In addition, semblance shares certain features of the summation, or "stack," method--a recently much-used coherence measure.

Several measures, including semblance, have been used in a seismic problem area--the determination of stacking velocities from multiple ground-coverage seismic data. A noise-free synthetic example was developed to compare discrimination thresholds of the various methods. Among the various coherence methods, the semblance calculation, if properly interpreted, has the greatest sensitivity.

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