科研之友
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摘要
To improve full waveform inversion (FWI) results for 2-D vertical transverse isotropic (VTI) media, we propose a new parameterization scheme that is based on Lame constants. In the new parameterization approach, elastic constants of C-11, C-13, C-33, and C-44 are replaced with Lame constants and newly introduced parameters of xi(1) and xi(2) for anisotropic properties. Multi-parametric inversion for elastic VTI media has been conducted using a two-step sequential inversion strategy, in which primary parameters (that are well inverted) are inverted first, and secondary parameters are inverted using the inverted primary parameters. In the conventional VTI parameterization approach, C-33 and C-44 are regarded as the primary parameters, whereas in the new parameterization approach, Lame constants are primary parameters. The new parameterization scheme is distinguished from the conventional VTI parameterization approach in scattering patterns of partial derivative wavefields with respect to primary parameters. Scattering patterns of Lame constants are similar to those of the isotropic case. Because Lame constants are well inverted in the isotropic case, they may also be well inverted in the new parameterization. On the other hand, we do not expect any direct improvements for anisotropic properties because xi(1) and xi(2) produce the same scattering patterns as those of C-11 and C-13. Gradient directions for a two-layered model show that we can improve the resolution of gradient direction for mu (one of the primary parameters). Although xi(1) and xi(2) of the new parameterization retain characteristics of C-11 and C-13 in the conventional parameterization, improved primary parameters (Lame constants) affect anisotropic parameters positively. Consequently, inversion results for all of the parameters can be improved. Numerical examples indicate that the new parameterization scheme provides more reliable inversion results than the conventional and sequential inversion approaches. In addition, the new parameterization approach exhibits higher degrees of computational efficiency than the sequential inversion approach because it involves simultaneous inversion of all parameters and does not require an additional inversion stage. Our new parameterization scheme can therefore overcome the intrinsic disadvantages of elastic inversion for VTI media. In applying the new parameterization to real seismic data, it is necessary to increase its applicability to noisy and low-frequency missing data and it also needs to be extended to 3-D case.
- 出版日期2014-10
