# Difference between revisions of "Coherency attribute stacks"

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Figure 3.2-41 shows portions of coherency attribute sections associated with a field data set. These sections, in conjunction with conventional stack, may be useful in enhancing fault patterns associated with structural plays and identifying amplitude anomalies associated with stratigraphic plays. Note the discriminating power of semblance for the most coherent reflection events in the section. Conventional [[CMP stacking]] seems to yield the most robust section that preserves reflections and diffrations. The coherency attribute sections based on crosscorrelation show an apparent higher frequency content compared to the stacked and normalized stacked sections. | Figure 3.2-41 shows portions of coherency attribute sections associated with a field data set. These sections, in conjunction with conventional stack, may be useful in enhancing fault patterns associated with structural plays and identifying amplitude anomalies associated with stratigraphic plays. Note the discriminating power of semblance for the most coherent reflection events in the section. Conventional [[CMP stacking]] seems to yield the most robust section that preserves reflections and diffrations. The coherency attribute sections based on crosscorrelation show an apparent higher frequency content compared to the stacked and normalized stacked sections. | ||

− | + | [[file:ch03_fig2-41.png|thumb| {{figure number|3.2-41}} Coherency attribute sections: (a) stack (equation {{EquationNote|16}}), (b) normalized stack (equation {{EquationNote|18}}), (c) unnormalized crosscorrelation (equation {{EquationNote|19}}), (d) normalized crosscorrelation (equation {{EquationNote|20}}), (e) energy-normalized crosscorrelation (equation {{EquationNote|21}}), and (f) semblance (equation {{EquationNote|22}}).]] | |

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− | + | ==Equations== | |

− | + | ||

− | + | {{NumBlk|:|<math>S=\sum\limits^M_{i=1}f_{i,t(i)},</math>|{{EquationRef|16}}}} | |

− | + | ||

− | </ | + | {{NumBlk|:|<math>NS=\frac{\sum\nolimits^M_{i=1}f_{i,t(i)}}{\sum\nolimits^M_{i=1}|f_{i,t(i)}|},</math>|{{EquationRef|18}}}} |

+ | |||

+ | {{NumBlk|:|<math>CC=\frac{1}{2}\sum\limits_t\left\{\left[\sum\limits^M_{i=1}f_{i,t(i)}\right]^2-\sum\limits^M_{i=1}f^2_{i,t(i)}\right\},</math>|{{EquationRef|19a}}}} | ||

+ | |||

+ | {{NumBlk|:|<math>CC=\frac{1}{2}\sum\limits_t\left[S^2_t-\sum\limits^M_{i=1}f^2_{i,t(i)}\right],</math>|{{EquationRef|19b}}}} | ||

+ | |||

+ | {{NumBlk|:|<math>NC=MF\sum\limits_t \sum\limits_{k=1}^{M-1}\sum\limits_{i=1}^{M-k}\frac{f_{i,t(i)}f_{i+k,t(i+k)}}{\sqrt{\sum\nolimits_t f^2_{i,t(i)}\sum\nolimits_t f^2_{i+k,t(i+k)}},}</math>|{{EquationRef|20}}}} | ||

+ | |||

+ | {{NumBlk|:|<math>EC=\frac{2}{(M-1)}\frac{CC}{\sum\nolimits_t\sum\nolimits^M_{i=1}f^2_{i,t(i)}}.</math>|{{EquationRef|21}}}} | ||

+ | |||

+ | {{NumBlk|:|<math>NE=\frac{1}{M}\frac{\sum\nolimits_t\sum\nolimits^M_{i=1}f_{i,t(i)}}{\sum\nolimits_t\sum\nolimits^M_{i=1}f^2_{i,t(i)}}.</math>|{{EquationRef|22a}}}} | ||

+ | |||

+ | {{NumBlk|:|<math>EC=\frac{1}{M-1}(M\times NE -1).</math>|{{EquationRef|22b}}}} | ||

==See also== | ==See also== |

## Latest revision as of 14:59, 18 September 2014

Series | Investigations in Geophysics |
---|---|

Author | Öz Yilmaz |

DOI | http://dx.doi.org/10.1190/1.9781560801580 |

ISBN | ISBN 978-1-56080-094-1 |

Store | SEG Online Store |

The various measures of coherency discussed in this section to compute velocity spectrum can also be used to generate coherency attribute stacks. These stacks are obtained as follows:

- Choose a specific measure of coherency — stacked amplitude (equation
**16**), normalized stacked amplitude (equation**18**), unnormalized crosscorrelation sum (equation**19**), normalized crosscorrelation sum (equation**20**), energy-normalized crosscorrelation sum (equation**21**), or semblance (equation**22**). - Compute velcoity spectra at selected CMP locations along the line and pick rms velocity functions.
- By interpolating between the vertical functions, derive an rms velocity section.
- Extract vertical rms velocity functions from the velocity section at each CMP location along the line traverse.
- Apply moveout correction to CMP gathers using the extracted vertical functions.
- Now, compute not just the stacked amplitudes (equation
**16**), but also the coherency attributes using equations (**18**) through (**22**) and thus obtain the coherency attribute sections.

Figure 3.2-41 shows portions of coherency attribute sections associated with a field data set. These sections, in conjunction with conventional stack, may be useful in enhancing fault patterns associated with structural plays and identifying amplitude anomalies associated with stratigraphic plays. Note the discriminating power of semblance for the most coherent reflection events in the section. Conventional CMP stacking seems to yield the most robust section that preserves reflections and diffrations. The coherency attribute sections based on crosscorrelation show an apparent higher frequency content compared to the stacked and normalized stacked sections.

## Equations

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## See also

- The velocity spectrum
- Measure of coherency
- Factors affecting velocity estimates
- Interactive velocity analysis
- Horizon velocity analysis
- Exercises
- Topics in moveout and statics corrections