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Book Chapter

Time-to-depth migration (TDM)

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Published:
January 01, 1980

Abstract

Traveltimes of CDP-stacked or time-migrated reflections tempt seismic in-terpreters to associate them directly with shapes of the reflecting horizons in depth. Such an association is certainly justified in areas of moderate geologic complexity. Moreover, time-migrated reflections often provide a good approx-imation of the true shape of seismic reflectors.

In the last two chapters, however, we showed that time-migrated seismic reflections, like CDP-stacked reflections, rarely fall precisely above their corre-sponding depth points. Lateral position errors in time migration are caused by lateral velocity changes above the reflectors of interest. We will refer, in general, to any of the many processes that transform from apparent positions on seismic time sections (whether stacked or time-migrated) to true positions in depth as time-to-depth migration (TDM).

It has long been recognized (Slotnick, 1936, 1959; Rice, 1949; Krey, 1951; Hagedoorn, 1954; Musgrave, 1964) that TDM is required for unmigrated data such as seismic records and sections of CDP-stacked or normal reflections. That TDM is also required for time-migrated reflections some readers may have realized (perhaps with some disappointment) only upon reading chapter 7. Whenever normal-incidence rays or image rays deviate from the vertical, a time-to-depth conversion that follows a CDP stack or time migration must have some form of TDM as a final step. In section 8.1, we briefly describe a TDM process for normal reflections. In sections 8.2 and 8.3, we show how to perform TDM for time-migrated reflections.

As we shall see in Chapter 9, the subject of computing interval velocities is also very

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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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