# Suppressing multiples by NMO differences

Series | Geophysical References Series |
---|---|

Title | Problems in Exploration Seismology and their Solutions |

Author | Lloyd P. Geldart and Robert E. Sheriff |

Chapter | 6 |

Pages | 181 - 220 |

DOI | http://dx.doi.org/10.1190/1.9781560801733 |

ISBN | ISBN 9781560801153 |

Store | SEG Online Store |

## Problem 6.11

A primary and a multiple each arrive at 0.600 s at ; their stacking velocities are 1800 and 1500 m/s, respectively. Calculate the residual NMO (after NMO correction for the primary velocity) for offsets of 300 , where . What is the shortest offset that will give good multiple suppression for a wavelet with a 50-ms dominant period?

### Solution

The distance to the primary reflector is and to the reflector responsible for the multiple, assuming it is simply a double bounce, is . NMO is given by equation (4.1c), . We obtain the following values for the moveouts:

Offset | 300 m | 600 m | 900 m |

Primary NMO | 0.023 s | 0.093 s | 0.208 s |

Multiple NMO | 0.033 s | 0.133 s | 0.300 s |

NMO Difference | 0.010 s | 0.040 s | 0.092 s |

Multiple suppression should be maximum when the NMO difference approximates half the wavelet period so that some of the traces are out-of-phase, which is achieved at offset where

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Differential moveout between primary and multiple | Distinguishing horizontal/vertical discontinuities |

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Geometry of seismic waves | Characteristics of seismic events |

## Also in this chapter

- Characteristics of different types of events and noise
- Horizontal resolution
- Reflection and refraction laws and Fermat’s principle
- Effect of reflector curvature on a plane wave
- Diffraction traveltime curves
- Amplitude variation with offset for seafloor multiples
- Ghost amplitude and energy
- Directivity of a source plus its ghost
- Directivity of a harmonic source plus ghost
- Differential moveout between primary and multiple
- Suppressing multiples by NMO differences
- Distinguishing horizontal/vertical discontinuities
- Identification of events
- Traveltime curves for various events
- Reflections/diffractions from refractor terminations
- Refractions and refraction multiples
- Destructive and constructive interference for a wedge
- Dependence of resolvable limit on frequency
- Vertical resolution
- Causes of high-frequency losses
- Ricker wavelet relations
- Improvement of signal/noise ratio by stacking