ABSTRACT
Common-image gathers are very useful for velocity and
amplitude analysis. Wavefield-extrapolation methods produce
Angle-Domain Common-Image Gathers (ADCIGs). For the conventional PP
case, ADCIGs are a function of the opening angle.
However, the ADCIGs for converted-wave data (PS-ADCIGs) are a
function of the half-aperture angle, that is, the incidence
angle plus the reflection angle.
In PS-ADCIGs, both the P-to-S velocity ratio ( ) and
the image dip play a major role in transforming
the subsurface offset into the opening angle.
We introduce a simple methodology to compute PS-ADCIGs.
Our methodology exploits the robustness of computing
PP-ADCIGs, and incorporates the velocity ratio ( ),
with an image dip field, which is estimated along the prestack
image. Our methodology also transforms the
half-aperture angle in PS-ADCIGs into an independent P-incidence angle to form
P-ADCIGs, and an independent S-reflection angle to form
S-ADCIGs.
Numerical studies show that when the
P-to-S velocity ratio and image midpoint information are not
incorporated, the
error in computing PS-ADCIGs is large enough to introduce
artifacts in the velocity model.
Synthetic results show the accuracy of the transformation
introduced in this paper. Real data results on the
2-D Mahogany field show the practical application
and implications for converted-wave angle-domain common-image
gathers.
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