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![]() | Nonhyperbolic reflection moveout of ![]() | ![]() |
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A transversely isotropic model with a vertical symmetry axis (VTI
medium) is the most commonly used anisotropic model for sedimentary
basins, where the deviation from isotropy is usually attributed to
some combination of fine layering and inherent anisotropy of
shales. One of the first nonhyperbolic approximations for the -wave
reflection traveltimes in VTI media was proposed by
Muir and Dellinger (1985) and further developed by
Dellinger et al. (1993). Thomsen (1986) introduced a
convenient parameterization of VTI media that was used by
Tsvankin and Thomsen (1994) to describe nonhyperbolic reflection moveouts.
We begin with an overview of the weak-anisotropy approximation for
-wave velocities in VTI media and use it for analytic derivations
throughout the paper. First, we consider a vertically heterogeneous
anisotropic layer. For this model, we compare the three-parameter
approximation for the
-wave traveltimes suggested by
Tsvankin and Thomsen (1994) with the shifted hyperbola (Malovichko, 1978; Castle, 1988; de Bazelaire, 1988). Next, we examine
-wave moveout in VTI media above
a curved reflector.
We analyze the cumulative action of anisotropy, reflector dip, and
reflector curvature, and develop an appropriate three-parameter representation
for the reflection moveout. Finally, we consider
models characterized by weak lateral heterogeneity and show that
it can mimic the influence of transverse isotropy on nonhyperbolic moveout.
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![]() | Nonhyperbolic reflection moveout of ![]() | ![]() |
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