Stacking

Seismic stacking is a key step in seismic data processing. It involves summing multiple seismic traces (typically from Common Midpoint [CMP] gathers) to produce a single trace that represents the subsurface reflectivity at that location. The main goal of stacking is to increase the signal-to-noise ratio (SNR) by reinforcing coherent signals (reflections) while suppressing random and incoherent noise.

Why is Stacking Needed?

When seismic waves are recorded:

• Each reflection event is recorded multiple times at different source-receiver offsets.
• Coherent reflection signals align properly if the correct Normal Moveout (NMO) correction is applied.
• Random noise, multiples, and other unwanted energy do not align coherently.
• Stacking sums these aligned signals, so the reflection signals add constructively, and random noise cancels out destructively     (by √N, where N = number of traces).

Basic Stacking Method

1. CMP Sorting
   • Gather traces that share the same midpoint.

1. Velocity Analysis
   • Estimate stacking velocity for each CMP gather.

1. NMO Correction
   • Apply Normal Moveout correction to flatten hyperbolic       reflection events.

1. Stacking (Simple Arithmetic Stack)
   • Sum or average the NMO-corrected traces       trace-by-trace.

Result: A single high SNR trace for each CMP.