# Translations:Rays/4/en

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Because the wavelength of light is very small compared with the size of ordinary objects, geometric optics can describe the behavior of a light in commonplace situations. When we turn to a seismic wave, the wavelength is not particularly small compared with the dimensions of geologic layers within the earth. However, the concept of a seismic ray fills an important need. Geometric seismology is not nearly as accurate as geometric optics, but ray theory can be used to solve many important practical geophysical problems. In particular, popular forms of prestack migration are based on tracing the raypaths of the primary reflections.