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Book Chapter

Physical and numerical model study of diffraction effects on seismic profiles over simple structures

By
D. R. Pant
D. R. Pant
School of Earth Sciences. Flinders University of South Australia. OPO Box 2100, Adelaide. South Australia 50U1.
Australia
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S. A. Greenhalgh
S. A. Greenhalgh
School of Earth Sciences. Flinders University of South Australia. OPO Box 2100, Adelaide. South Australia 50U1.
Australia
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B. Zhou
B. Zhou
School of Earth Sciences. Flinders University of South Australia. OPO Box 2100, Adelaide. South Australia 50U1.
Australia
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Published:
January 01, 2016

Summary

2-D scale models and synthetic seismograms have been used to study diffraction artifacts and interpretation pitfalls on seismic profiles over two classes of simple-shaped structures: a vertical fault model and a rectangular mound model.

The fault throw was varied from one eighth of a wavelength (A/8) to two wavelengths (2A). For throws greater than A/2, the structure is resolved in the x-t domain but diffractions which are present convey misleading structure. Amplitude and wavelet anomalies are observed for small fault displacement (<A/2) which serve to detect but not to define the exact fault position and extent. Migration improves but does not necessarily overcome the problem.

Mound structures having heights of A/8 to 2A, and length of one half to twice the Fresnel zone radius, were investigated. Lateral resolution is improved as the length of the structure increases, but only for mounds which are vertically resolved (height greater than A/2). For low relief mounds, resolution deteriorates with increasing mound length. The resulting edge diffractions, which interfere with the reflection events, serve to detect and identify the target. Amplitude anomalies are observed across the structures, but it is not possible (without calibration) to interpret the edges of the model. Even for thick mounds the diffraction patterns complicate the seismic picture and can lead to false interpretation.

The migration aperture needs to be about 10 times the Fresnel zone radius to produce satisfactory results. However, for vertically unresolved structures, migration may not significantly help. Complicating factors with post-stack migration are lack of knowledge of the true velocity function and inadequacy of the CMP zero-offset equivalence assumption.

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Contents

Society of Exploration Geophysicists Geophysics Reprint Series

Seismic Diffraction

Kamil Klem-Musatov
Kamil Klem-Musatov
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Henning Hoeber
Henning Hoeber
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Michael Pelissier
Michael Pelissier
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Tijmen Jan Moser
Tijmen Jan Moser
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Society of Exploration Geophysicists
Volume
30
ISBN electronic:
9781560803188
Publication date:
January 01, 2016

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