The phenomenon of amplitude variation with offset (AVO) of seismic reflection data is commonly assumed to occur only due to the petrophysical properties of the reflecting interfaces [Sheriff and Geldart (1995); Yilmaz (2001)]. However, amplitude can vary with offset due to absorption, or to focusing through velocity anomalies which are too small to give full triplications. The latter phenomenon has been shown to occur in several 2D [Kjartansson (1979); Harlan (1994)] and 3D Hatchell (2000a) seismic datasets. We will call it ``focusing effect AVO'' (FEAVO). FEAVO differs in two respects from regular AVO: 1) in CMP gathers, the high amplitudes are accompanied by local departures from hyperbolic moveout in the reflected arrivals (See Figure 1a); and 2) in the midpoint-offset space, the high amplitudes are distributed in ``V'' patterns whereas regular AVO gives rectangular patterns (See Fig. 1b). We must remove the FEAVO in order to allow AVO studies on FEAVO-affected data. Thus, it is necessary to:
Devise and prove the feasibility of a method whose application to FEAVO-affected 2D and 3D datasets would produce a velocity field accurate enough to generate a FEAVO-free prestack volume by downward continuing the wavefield through the FEAVO-generating anomalies.