TURNING WAVE MIGRATION BY HORIZONTAL EXTRAPOLATION

Conventional migration based on depth stepping extrapolation fails to migrate turning wave energy because of its inability to propagate ener gy with dips beyond 90 degrees. A viable strategy for imaging turning waves is to use horizontal, rather than depth, extrapolation. This can be implemented by a 90 degrees rotation of the extrapolator so that t he data are extrapolated horizontally rather than vertically. In this geometry, the energy associated with turned rays consistently moves in the same direction as the extrapolation, and so only one pass is nece ssary to image turned reflections. The viability of this strategy is d emonstrated with both synthetic and field poststack data that include turned reflections from salt flanks. Depth extrapolation images the ne ar-horizontal structure and horizontal extrapolation images the near-v ertical structure, and combining them gives a full image containing al l dips.