# Difference between revisions of "Suppressing multiples by NMO differences"

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− | == Problem == | + | == Problem 6.11 == |

A primary and a multiple each arrive at 0.600 s at <math>x=0</math>; 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 <math>n</math>, where <math>n=1, 2,...</math>. What is the shortest offset that will give good multiple suppression for a wavelet with a 50-ms dominant period? | A primary and a multiple each arrive at 0.600 s at <math>x=0</math>; 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 <math>n</math>, where <math>n=1, 2,...</math>. What is the shortest offset that will give good multiple suppression for a wavelet with a 50-ms dominant period? | ||

## Latest revision as of 15:22, 8 November 2019

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 **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle x=0}**
; 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 **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle n}**
, where **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle n=1, 2,...}**
. 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 **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle (0.600\times 1800)/2=540\ {\rm m}}**
and to the reflector responsible for the multiple, assuming it is simply a double bounce, is **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle (0.600\times 1500)/4=225\ {\rm m}}**
. NMO is given by equation (4.1c), **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \Delta t_{\rm NMO} =x^{2} /2V^{2} t_{0}}**
. 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 **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle x}**
where

**Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \begin{align} x^{2} /1.200\times 1500^{2} -x^{2} /1.200\times \; 1800^{2}\; =0.050,\; x =660\ {\rm m}. \end{align} }**

## Continue reading

Previous section | Next section |
---|---|

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

Previous chapter | Next chapter |

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