Deducing geologic significance from the aggregate of many minor observations tests the ingenuity of an interpreter and his in-depth understanding of physical principles. For example, downdip thinning of reflection intervals might result from a normal increase of velocity with depth as well as from sediment thinning, and flow of salt or shale may cause illusory structure on deeper horizons. Geometric focusing produced by reflector curvature can produce various effects, especially if the data have not been migrated correctly, and energy that comes from a source located off to one side of the line can interfere with the patterns of other reflection events to produce effects that might be interpreted erroneously, unless their true nature is recognized. Improper processing likewise can create opportunities for misinterpreting data。