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| Titel |
PS wave image enhancement using polarity reversal correction in the wavenumber domain |
| VerfasserIn |
Byoung Yeop Kim, Ho Young Lee, Nam Hyung Koo, Snons Cheong, Soon Jee Seol, Joongmoo Byun |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108073
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| Publikation (Nr.) |
 EGU/EGU2015-7804.pdf |
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| Zusammenfassung |
| Polarities of the S waves are reversed at all reflection points, therefore these reversals should
be considered in elastic imaging of multicomponent seismic data. If the polarity reversals of S
wave are not corrected properly, the final PS image generated by summing over every shot
domain migration may deteriorate. If the underground structure is horizontally layered, then
the polarities of the S wave are reversed at the zero offset. However, in heterogeneous media,
such as real Earth’s interior, defining where the S wave polarities are reversed is complex.
Many elastic migration methods correct polarity reversals in the angle domain by reversing
the sign of the negative angle data or by calculating the sign factor using the energy flux
density vector to correct the polarity reversal. These are all implemented in the spatial
domain.
In this study, the reversed S wave polarities are corrected in the wavenumber domain
using simple equation then imaged in the frequency-spatial domain using elastic
generalized-screen migration algorithm. The reflection angle at the underground reflector is
represented using the wavenumber basis according to the expressions as tan γ = -kh/kz,
where γ is the reflection angle and kh and kz are offset wavenumber and depth wavenumber,
respectively. According to the Equation, the sign of the reflection angle can be expressed as
-1x(sign of horizontal wavenumber); therefore, the S wave polarities can be easily corrected
in the wavenumber domain by reversing the sign of the extrapolated wave on one side of the
position at kx = 0. Subsequently, the wavefields are inverse Fourier transformed to the
frequency-spatial domain, and then, the imaging condition is applied. This method is very
efficient in thin-slab way migration algorithm such as phase-screen or generalized-screen
migration. For the verification, simple horizontal 2-layer and tilted model were
tested using the elastic generalized-screen migration algorithm. Furthermore, the
effect of the S wave polarity corrections on the more realistic complex model is
also tested using the SEG/EAGE salt model. All PS wave images after polarity
reversal corrections using our method show clearer events with exact positions. |
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