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Book Chapter

Time migration

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Published:
January 01, 1980

Abstract

Exploration seismologists base their interpretation, skill, and judgment largely on the study of primary reflections for selected key horizons on time sections. These horizons are normally available in either CDP-stacked (i.e., unmigrated form) or time-migrated form. In regions of complex structure, the two forms of reflection can be markedly different; that is, at a common surface location the associated traveltimes to a particular reflector can differ considerably. Properly time-migrated sections can be expected to provide more realistic pictures of the geologyߝpictures which may not be simply inferred from their unmigrated counterparts, the CDP-stacked sections. The underlying principles of time migration are well described in the literature. We will, therefore, discuss only those ray-theoretical aspects that will assist later in better understanding problems related to computing interval velocities from migration velocities.

Various time migration schemes are used nowadays to transform either a CDP stacked section or common-offset sections obtained along a seismic line into a time-migrated section. One basic approach (known variously as Kirchhoff migration, Huygens-Fresnel migration, and diffraction migration) involves sum-ming scattered signals (in a weighted manner) into the apex of diffraction curves. This approach is founded on the Kirchhoff integral solution to the wave equation. It can be implemented in various ways, all of which lead to almost identical results. In the presence of strong lateral velocity gradients, however, such schemes fail to position reflections correctly (sometimes grossly so) and in that sense fail to serve the desired function of migration. The terminology originated, however, at a time when

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Contents

Interval Velocities from Seismic Reflection Time Measurements

Peter Hubral
Peter Hubral
Bundesanstalt fiir Geowissenschaften und Rohstoffe Rohstoffe Hannover, West Germany
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Theodor Krey
Theodor Krey
Consultant Prakla-Seismos Hannover, West Germany
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L.Larner Kenneth
L.Larner Kenneth
Western Geophysical Company Houston, Texas
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Society of Exploration Geophysicists
ISBN electronic:
9781560802501
Publication date:
January 01, 1980

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