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REFLECTION AMPLITUDES AND MIGRATION AMPLITUDES (ZERO‐OFFSET SITUATION) 1
Author(s) -
BORTFELD R.,
KIEHN M.
Publication year - 1992
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.1992.tb00557.x
Subject(s) - amplitude , overburden , reflection (computer programming) , amplitude versus offset , continuation , reflection coefficient , zero (linguistics) , offset (computer science) , inverse , half space , geology , physics , seismic migration , mathematical analysis , geometry , mathematics , geophysics , optics , philosophy , computer science , linguistics , programming language , mining engineering
A bstract The effect of wave‐equation migration on amplitudes is determined. This effect is derived for zero‐offset traces and for second‐order approximations of the traveltimes. Three steps are followed: firstly, the amplitudes of zero‐offset traces are established; secondly minus half the traveltimes are used as input for downward continuation in migration (forward in space and time); thirdly, the amplitudes of the migrated events are determined by downward continuation (at zero‐traveltimes). Layered models (piles of homogeneous layers) with smooth interfaces are used. The determinants of the 2 × 2 matrices B 0 obtained for these models are responsible for the main effect on migration. The migration result primarily depends on the overburden as the inverse of det ( B 0 ). Drastic effects can occur over small distances. For weakly reflecting media, it is confirmed that wave‐equation migration gives “correct” results (but the input data must be multiplied by V 0 T 0 ), i.e. amplitudes proportional to the reflection coefficient. For any velocity changes, the inverse of det ( B 0 ) will, in general, give inaccurate migration amplitudes and inaccurate lithological interpretations. In a simple step, true amplitude migration, or exact migration, is derived from our results. It is assumed that no focus phenomena are present. The effect of buried foci is discussed briefly.