Imaging tilted transversely isotropic media with a generalised screen propagator
Sung-Il Shin 1 Joongmoo Byun 2 3 Soon Jee Seol 21 SK Building, 26 Jongno, Jongno-gu, Seoul, 110-728, Korea.
2 Department of Natural Resources and Geoenvironmental Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul, 133-791, Korea.
3 Corresponding author. Email: jbyun@hanyang.ac.kr
Exploration Geophysics 46(4) 349-358 https://doi.org/10.1071/EG14113
Submitted: 11 November 2014 Accepted: 12 November 2014 Published: 13 January 2015
Abstract
One-way wave equation migration is computationally efficient compared with reverse time migration, and it provides a better subsurface image than ray-based migration algorithms when imaging complex structures. Among many one-way wave-based migration algorithms, we adopted the generalised screen propagator (GSP) to build the migration algorithm. When the wavefield propagates through the large velocity variation in lateral or steeply dipping structures, GSP increases the accuracy of the wavefield in wide angle by adopting higher-order terms induced from expansion of the vertical slowness in Taylor series with each perturbation term. To apply the migration algorithm to a more realistic geological structure, we considered tilted transversely isotropic (TTI) media. The new GSP, which contains the tilting angle as a symmetric axis of the anisotropic media, was derived by modifying the GSP designed for vertical transversely isotropic (VTI) media. To verify the developed TTI-GSP, we analysed the accuracy of wave propagation, especially for the new perturbation parameters and the tilting angle; the results clearly showed that the perturbation term of the tilting angle in TTI media has considerable effects on proper propagation. In addition, through numerical tests, we demonstrated that the developed TTI-GS migration algorithm could successfully image a steeply dipping salt flank with high velocity variation around anisotropic layers.
Key words: anisotropy, generalised screen, prestack migration, tilted transversely isotropic.
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