Scaled physical models have rapidly become recognized as an efficient way in which some geologic problems can be approached.

Models were originally built of readily malleable materials, and at first these models represented simplistic geologic features such as domes or two-dimensional synclines. The models were then immersed in a water tank where ultrasonic transducers were passed over them in such a way that the data resembled those collected by a seismic crew on the surface of the earth. These sets of data were used in the development of some of the earliest successful three-dimensional migration programs. It soon became apparent that the single interface of the early models could be replaced by layered models which more nearly resembled sedimentary sequences of rocks. Such models became very useful in developing interactive interpretation devices with which cubes of seismic information could be examined rom different vantage points. This improvement was a definite aid to interpretation.

Recently it has become clear that the physical modeling technique can be applied just as readily to lithologic problems. Subtle changes in physical properties can manifest themselves on the model seismic section just as they do on the real sections.

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