Comparison of the FORT approximation of the coupling ray theory with the Fourier pseudospectral method |
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| Authors: | Ivan P?en?ík Véronique Farra Ekkehart Tessmer |
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| Institution: | (1) Department of Geophysics, Mathematics and Physics, Charles University, Ke Karlovu 3 121 16, Praha, Czech Republic;(2) Institute of Geophysics, Academy of Sciences of Czech Republic, Bočn? II 141 31, Praha, Czech Republic |
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| Abstract: | The standard ray theory (RT) for inhomogeneous anisotropic media does not work properly or even fails when applied to S-wave
propagation in inhomogeneous weakly anisotropic media or in the vicinity of shear-wave singularities. In both cases, the two
shear waves propagate with similar phase velocities. The coupling ray theory was proposed to avoid this problem. In it, amplitudes
of the two S waves are computed by solving two coupled, frequency-dependent differential equations along a common S-wave ray.
In this paper, we test the recently developed approximation of coupling ray theory (CRT) based on the common S-wave rays obtained
by first-order ray tracing (FORT). As a reference, we use the Fourier pseudospectral method (FM), which does not suffer from
the limitations of the ray method and yields very accurate results. We study the behaviour of shear waves in weakly anisotropic
media as well as in the vicinity of intersection, kiss or conical singularities. By comparing CRT and RT results with results
of the FM, we demonstrate the clear superiority of CRT over RT in the mentioned regions as well as the dangers of using RT
there. |
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