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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
[(); ()]. 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 [();
()] and 3D () 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 a); and 2) in the midpoint-offset space, the
high amplitudes are distributed in ``V'' patterns whereas
regular AVO gives rectangular patterns (See
Fig. b). 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.
Next: Motivation
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Stanford Exploration Project
6/7/2002