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Velocity Modeling in a Vertical Transversely Isotropic Medium Using Zelt Method | ||
| AUT Journal of Modeling and Simulation | ||
| مقاله 5، دوره 43، شماره 1، تیر 2011، صفحه 35-40 اصل مقاله (429.67 K) | ||
| نوع مقاله: Research Article | ||
| شناسه دیجیتال (DOI): 10.22060/miscj.2011.148 | ||
| چکیده | ||
| In the present paper, the Zelt algorithm has been extended for ray tracing through an anisotropic model. In anisotropic media, the direction of the propagated energy generally differs from that of the plane-wave propagation. This makes velocity values to be varied in different directions. Therefore, velocity modeling in such media is completely different from that in an isotropic media. The velocity model for ray tracing is parameterized in terms of blocky trapezoid cells where the velocity changes inside the cells linearly. Thomsen’s approximations in weakly anisotropic media were used to estimate anisotropic velocity vectors. Rays were traced in direction of group vector in the vertical transversely isotropic (VTI) media, whereas, the anisotropic Snell’s law must be satisfied by the phase angle and phase velocities across the interface. The synthetic examples are given to demonstrate and verify the ray tracing algorithm. Reflected and turning waves were traced through the isotropic and anisotropic velocity models. Lateral and vertical velocity variation caused deviation on trajectory of the traveltime curve. The results show that the difference between isotropic and anisotropic traveltimes increases with offset, especially when the ratio offset/depth exceeds 1.5. | ||
| کلیدواژه‌ها | ||
| Ray tracing؛ Vertical Transversely Isotropy (VTI)؛ Zelt method؛ seismic velocity modeling | ||
| عنوان مقاله [English] | ||
| Velocity Modeling in a Vertical Transversely Isotropic Medium Using Zelt Method | ||
| چکیده [English] | ||
| In the present paper, the Zelt algorithm has been extended for ray tracing through an anisotropic model. In anisotropic media, the direction of the propagated energy generally differs from that of the plane-wave propagation. This makes velocity values to be varied in different directions. Therefore, velocity modeling in such media is completely different from that in an isotropic media. The velocity model for ray tracing is parameterized in terms of blocky trapezoid cells where the velocity changes inside the cells linearly. Thomsen’s approximations in weakly anisotropic media were used to estimate anisotropic velocity vectors. Rays were traced in direction of group vector in the vertical transversely isotropic (VTI) media, whereas, the anisotropic Snell’s law must be satisfied by the phase angle and phase velocities across the interface. The synthetic examples are given to demonstrate and verify the ray tracing algorithm. Reflected and turning waves were traced through the isotropic and anisotropic velocity models. Lateral and vertical velocity variation caused deviation on trajectory of the traveltime curve. The results show that the difference between isotropic and anisotropic traveltimes increases with offset, especially when the ratio offset/depth exceeds 1.5. | ||
| کلیدواژه‌ها [English] | ||
| Ray tracing, Vertical Transversely Isotropy (VTI), Zelt method, seismic velocity modeling | ||
| مراجع | ||
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[1] J.G. Berryman, “Long-wave elastic anisotropy in transversely isotropic media,” Geophysics, vol. 44, pp. 896-917, 1979. [2] V. Cerveny, I.A. Molotkov, and I. Psencik, Ray method in seismology, Universita Karlova, 1977. [3] V. Cerveny, The application of raytracing to the numerical modeling of seismic wavefields in complex structures, Handbook of geophysical exploration, Geophysical Press, London, 1985. [4] V. Grechka, I. Tsvankin, “PP+PS=SS,” Geophysics, vol. 67, pp. 1961-1971, 2002. [5] K. Helbig, “Systematic classification of layer-induced transverse isotropy,” Geophy. Prosp., vol. 29, pp. 550-577, 1981. [6] K. Helbig, Foundations of anisotropy for exploration seismic. Handbook of Geophysical Exploration. Oxford, Pergamon, 1994. [7] B.R. Julian, and D. Gubbins, “3-D seismic ray tracing,” Geophysics, vol. 43, pp. 95-113, 1977. [8] Th. Krey, K. Helbig, “A theorem concerning anisotropic stratified media and its significance for reflection seismic,” Geophy. Prosp., vol. 4, pp. 294- 302, 1956. [9] F.K. Levin, “The reflection, refraction of waves in media with elliptical velocity dependence,” Geophysics, vol. 43, pp. 528- 537, 1978. [10] A. Lomax, “Wavelength-smoothing method for approximating broad-band wave propagation through complicated velocity structures,” Geophysics. J. Int., vol. 117, pp. 313-334, 1994. [11] T. J. Moser, “Shortest path calculation of seismic rays,” Geophysics, vol. 59, pp. 59-67, 1991. [12] P. Podvin, and I. Lecomte, “Finite difference computation of traveltimes in very contrasted velocity models: a massively parallel approach and its associated tools,” Geophys. J. Int., vol. 105, pp. 271-284, 1991. | ||
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