The nice looking seismic sections you’re used to seeing in text books are compiled from field data which is collected in the form of shot records. The disturbances you see in this record consist of different wave types and also of energy traveling along different paths between the source and receiver.

Miller et al. 1995

Recall Ray-Trace Exercise IV The simulated normal incidence ray-paths have the potential to provide a more accurate visual image of the subsurface.

Here’s an example of such a data set; the shot locations are obvious aren’t they. We now have a nice geologic looking seismic section. Can you spot the inversion structure?

source receiver layouts used to acquire common midpoint data. Shooting Geometries source receiver layouts used to acquire common midpoint data. Very often these layouts are asymmetrical

Common Midpoint Data Reflections share the same midpoint and in this case (horizontal reflector) they also share a common reflection point or depth point

Three traces in this case (a three fold data set) get summed together to yield one stack trace. The Stack Trace

Why go to all the trouble of collecting duplicate data?

Some inherent difficulties

The resulting stack trace

Consider what happens across the axis of the syncline and the relation of recording points to reflection points.

The record of reflection travel time to the various points in the subsurface contains dramatic image distortions - instead of a syncline we have an anticline