A physical model study of the travel times and reflection points of SH-waves reflected from transversely isotropic media with tilted symmetry axes
Li-Chung Sun 1 Young-Fo Chang 2 4 Chih-Hsiung Chang 3 Chia-Lung Chung 21 Department of Electrical Engineering, Nan Kai Institute of Technology, Nantou 54210, Taiwan.
2 Institute of Seismology, National Chung Cheng University, Chiayi 62102, Taiwan.
3 General Education Center, National Chiayi University, Chiayi 62103, Taiwan.
4 Corresponding author. Email: seichyo@ccu.edu.tw
Exploration Geophysics 43(3) 149-155 https://doi.org/10.1071/EG10033
Submitted: 29 October 2010 Accepted: 18 April 2012 Published: 23 May 2012
Abstract
In reflection seismology, detailed knowledge of how seismic waves propagate in anisotropic media is important for locating reservoirs accurately. The SH-wave possesses a pure mode polarization which does not convert to P- and SV-waves when reflecting from a horizontal interface, and vice versa. The simplicity of the SH-wave thus provides an easy way to view the details of SH-wave propagation in anisotropic media. In this study, we attempt to inspect the theoretical reflection moveouts of SH-waves reflected from transversely isotropic (TI) layers with tilted symmetry axes and to verify the reflection point, which could be shifted away from the common midpoint (CMP), by numerical calculations and physical modelling.
In travel time-offset analyses, the moveout curves of SH-waves reflected from horizontal TI media (TIM) with different tilted angles of symmetry axes are computed by the TI modified hyperbolic equation and Fermat’s principle, respectively. It turns out that both the computed moveout curves are similar and fit well to the observed physical data. The reflection points of SH-waves for a CMP gather computed by Fermat’s principle show that they are close to the CMP for TIM with the vertical and horizontal symmetry axes, but they shift away from the CMP for the other tilted angles of symmetry axes. The shifts of the reflection points of the SH-waves from the CMP were verified by physical modelling.
Key words: CMP, Fermat’s principle, hyperbolic moveout, SH-waves, transversely isotropic media.
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