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Book Chapter

Stacking-velocity analysis

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Published:
January 01, 1980

Abstract

In the preceding chapters we largely made use of ray-theoretical concepts and emphasized various algorithms for computing interval velocities from traveltime measurements. Now we will consider some more practical aspects of computing interval velocities from CDP reflection time measurements. We will outline some procedures that should be adhered to in order successfully to apply the generalized "Dix-type" formulas established above to measurements obtained in a real (geo-) physical world. Foremost, our traveltime inversion algorithms require that the real earth be closely approximated by the models considered above.

As in many other inversion algorithms, "idealized" surface measurements are required; such measurements are derived from "real" surface measurements only after applying certain corrections. Geophysicists who have previously computed interval velocities from either stacking- or migration velocities know that, typically, a host of often maddening problems is encountered when working with real seismic data. Some of these problems result from applying invalid corrections to the surface measurements.

The most critical parameter that must be obtained from CDP reflections is the NMO velocity VNMO. At best, it equals the stacking velocity Vs for infinitesimal small offset only. A number of factors influence and bias VNMO and Vs. These quantities are commonly computed in the digital computer by a procedure known as a stacking-velocity analysis (SVA).

A successful SVA requires adequately preprocessing CDP gathers and choosing some coherency measure for the computation of velocity spectra. Picking, validation, and smoothing schemes may follow after the spectra are computed. In addition to providing estimates of Vs', these

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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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