False semicircles in migrated data

Dip filtering can be used to suppress multiples. Chapter will show that multiples are unlike primaries in one important respect: their strength may change rapidly in the horizontal direction. They need not be spread out into broad diffraction hyperbolas as primaries must. This difference arises because multiples often spend much time focusing themselves in the irregular, near-surface areas. Common evidence for this behavior is contained in the appearance of wide-angle migrated sections. Such sections often show semicircular arcs coming all the way up to the surface. These arcs warn that something is wrong. The arcs could result from multiples, statics, or unexplained impulsive noise. In any case, they could be partially suppressed without touching primaries.