Effects of the symmetry axis orientation of a TI overburden on seismic images
Chih-Hsiung Chang 1 3 Young-Fo Chang 2 Cheng-Wei Tseng 21 General Education Center, and Center of Energy Research and Sensor Technology – National Chiayi University, No. 300 Syuefu Road, Chiayi City 60004, Taiwan.
2 Institute of Seismology, National Chung Cheng University, No. 168, Sec. 1, University Road, Min-Hsiung Township, Chia-yi County 621, Taiwan.
3 Corresponding author. Email: charles@mail.ncyu.edu.tw
Exploration Geophysics 48(4) 449-455 https://doi.org/10.1071/EG15124
Submitted: 1 December 2015 Accepted: 11 May 2016 Published: 7 July 2016
Journal Compilation © ASEG Open Access CC BY-NC-ND
Abstract
In active tectonic regions, the primary formations are often tilted and subjected to the processes of folding and/or faulting. Dipping formations may be categorised as tilted transverse isotropy (TTI). While carrying out hydrocarbon exploration in areas of orogenic structures, mispositioning and defocusing effects in apparent reflections are often caused by the tilted transverse isotropy of the overburden. In this study, scaled physical modelling was carried out to demonstrate the behaviours of seismic wave propagation and imaging problems incurred by transverse isotropic (TI) overburdens that possess different orientations of the symmetry axis. To facilitate our objectives, zero-offset reflections were acquired from four stratum-fault models to image the same structures that were overlain by a TI (phenolite) slab. The symmetry axis of the TI slab was vertical, tilted or horizontal. In response to the symmetry axis orientations, spatial shifts and asymmetrical diffraction patterns in apparent reflections were observed in the acquired profiles. Given the different orientations of the symmetry axis, numerical manipulations showed that the imaged events could be well described by theoretical ray paths computed by the trial-and-error ray method and Fermat’s principle (TERF) method. In addition, outputs of image restoration show that the imaging problems, i.e. spatial shift in the apparent reflections, can be properly handled by the ray-based anisotropic 2D Kirchhoff time migration (RAKTM) method.
Key words: anisotropic migration, physical model, structure image, tilted transverse isotropy.
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