Re: AVO on stacked gathers
Okay - an old post, but one with no reply.
You can only do AVO or AVA analysis on unstacked data - that is to say gathers, before they are stacked.
This is because you need to have offsets (AVO) or angles (AVA) available for these analysis techniques - they use the fact that the amplitude of the seismic reflection will vary with angle (based on the Zeoppritz equations) which might give you detectable variations that can be used to predict oil or gas. In AVO analysis they are approximating the angle with offset.
When you stack the data, you add up all the traces in the pre-stack gather, usually after correcting them to zero offset (via NMO correction or pre-stack migration); as such you don't have a gather any more, just stacked traces.
The stacked traces don't have any offset or angle information any more - so AVO and AVA analysis is not possible.
You can use other techniques with stacked data - such as acoustic or elastic impedance inversion.
It is also possible to *partially* stack the data into a series of "offset limited stacks" - or more commonly "angle stacks"; these are usually used for "AVO reconnaissance" as you can compare the nears (angles /offsets) to the fars (angle offsets) and look for differences that show an AVO/AVA anomaly for further investigation.