1887

Abstract

Seismic anisotropy observed in the field is a cumulative result of various mechanisms. Subsurface rocks often<br>possess intrinsic anisotropy approximated by a transversely isotropic solid with a vertical symmetry axis (VTI).<br>Alternatively, in the long-wavelength limit, ”layer-induced” VTI anisotropy may arise even in a stack of thin isotropic<br>constituent layers. In most practical cases these two effects occur simultaneously. We develop weak anisotropy and<br>weak contrast approximations to understand the contributions of intrinsic and layer-induced anisotropy. When the<br>contrast in elastic parameters between the constituents is small and their anisotropy is weak, then (to the first order)<br>layering-induced anisotropy is insignificant whereas intrinsic anisotropy produces effective Thomsen parameters equal<br>to the thickness-weighted average of the interval anisotropy parameters. This conclusion considerably simplifies<br>upscaling of finely-layered VTI media because to find the effective Thomsen parameter ² (or ± or °) one needs to<br>know only constituents ²’s (or ±’s or °’s correspondingly).<br>For larger variation in the elastic properties, each anisotropic parameter may be approximated as the sum of two<br>terms: one is the averaged intrinsic anisotropy and the other is a purely isotropic term related to fluctuations in<br>the vertical interval velocities. The isotropic term has been extensively investigated in literature, and all previous<br>conclusions may be directly applied to the more realistic VTI case considered in this study.

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/content/papers/10.3997/2214-4609-pdb.38.F053
2003-09-01
2020-10-27
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.38.F053
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