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Lets consider this in marine seismic processsing. I am assuming you know what a first order primary reflection is, if not, I can define it.

Ok, so if we were to have a source $(S)$ and receiver $(R)$ lying directly on the $x$ axis seperated with a distance of $n$ meters, and a horzontial reflective surface, then the reflection point for a first order multiple would lie at the mid point $S$ and $R$, i.e at the point $\frac{n}{2}$. However, if we were to have a dip of a certain angle in the $x$ direction, then now our reflection point would change. The "aperture" is a range in which the new reflection point could lie in.

As this is done in the deep water marine environment, we might not know the exact angle of the wave as it goes down and the exact angle of the dip of the reflector, so how would we come up with an aperture to cover the possible location of the surface reflection point? In this case, the aperture will just be a line.

Similarly, if there was a dip in the $y$ direction, how would we come up with an aperture that could help us cover the surface reflection point?

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Hardy's "Basic Seismic Processing for Interpreters" has a chapter called "Migration in Practice" that addresses your question in a general way.

As a personal aside, your question reminded me of my early career in northern Canada exploring for oil on a reflection seismic crew in the 1950s.

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  • $\begingroup$ Could you say a word or two about what to look for or what words are important? Without that this is pretty near a "link only" answer. A good one and very helpful, I'm sure, but I would like to discourage them in general. $\endgroup$ – dmckee Dec 25 '13 at 1:57
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If you're currently doing marine seismic data processing and do not have Ozdogan Yilmaz's "Seismic Data Processing", please grab a copy! It's more thoroughly discussed in there (pages 269 and 389).

In general we need to use all the available information to determine the migration aperture so a regional velocity model as well as any information about the maximum structural dip of the area can be used (eg. from well logs).

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