Lect 11: Stacking

Lect 11: Stacking

1. Where did it come from??

   • Pre-Stack Time Migration
     • After Migration section
   • Post- Stack Time Migration
     • Before Migration section

2. 2 Types of Stacking Process:

   • Horizontal Stacking : Stack in horizontal direction by sum of the NMO corrected data
     • NMO corrected data that obtain from velocity analysis being use for the horizontal
   • Vertical Stacking: Add & average the seismic record over same shot position
     • Stack on a particular seismic trace. (Rarely use - as will not give clear representative of subsurface)

3. The result is an approximation of a zero-offset section, where reflections come from below the CMP postion

4. Objectives of Stacking process:

   • A true representation of Earth's subsurface
   • Improve Signal-to-Noise ratio
   • Attenuate multiples
   • Reduce data volume

5. Stacking Method

   • Mean Stack
     • All NMO-corrected traces are summed and divided by the number of traces:
   • Weighted Stack
     • Unequal weighting of the traces
     • May yield better results.
     • Suitable for traces contain a lot of noise
     • Often used to suppress multiples
     • Need to introduce a weight factor.
     • Most use in industry
   • Diversity stacking / Min-Max-exclude (rarely use)
     • Certain traces are muted and not included in the stacking procedure
     • When certain values differ too much from the average value they can be muted (diversity stacking). this to reduce the influence of spikes
     • Exclusion of traces with the minimum and maximum amplitudes in the stacking procedure (min-max-exclusion or alpha-trimmed stack)

6. Effect of Velocity

   • NMO V: 1700 m/s good stack response
   • NMO V: 1500 m/s event overcorrected poor stack response
   • NMO V: 2000 m/s event undercorrected poor stack response

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