Abstract
Orthorhombic anisotropic model inversion is extra challenging
because of the multiple parameter nature of the inversion
problem. The high number of parameters required to describe
the medium exerts considerable trade-off and additional nonlinearity
to a full-waveform inversion (FWI) application. Choosing
a suitable set of parameters to describe the model and
designing an effective inversion strategy can help in mitigating
this problem. Using the Born approximation, which is the central
ingredient of the FWI update process, we have derived radiation
patterns for the different acoustic orthorhombic
parameterizations. Analyzing the angular dependence of scattering
(radiation patterns) of the parameters of different parameterizations
starting with the often used Thomsen-Tsvankin
parameterization, we have assessed the potential trade-off between
the parameters and the resolution in describing the
data and inverting for the parameters. The analysis led us to introduce new parameters ϵd, δd, and ηd, which have azimuthally
dependent radiation patterns, but keep the scattering potential
of the transversely isotropic parameters stationary with
azimuth (azimuth independent). The novel parameters ϵd, δd,
and ηd are dimensionless and represent a measure of deviation
between the vertical planes in orthorhombic anisotropy. Therefore,
these deviation parameters offer a new parameterization
style for an acoustic orthorhombic medium described by six
parameters: three vertical transversely isotropic (VTI) parameters,
two deviation parameters, and one parameter describing the
anisotropy in the horizontal symmetry plane. The main feature
of any parameterization based on the deviation parameters, is
the azimuthal independency of the modeled data with respect
to the VTI parameters, which allowed us to propose practical
inversion strategies based on our experience with the VTI
parameters. This feature of the new parameterization style holds
for even the long-wavelength components of the model constrained
by traveltimes.
| Original language | English (US) |
|---|---|
| Pages (from-to) | R157-R171 |
| Number of pages | 1 |
| Journal | GEOPHYSICS |
| Volume | 81 |
| Issue number | 4 |
| DOIs | |
| State | Published - Jun 2 2016 |
Bibliographical note
KAUST Repository Item: Exported on 2020-10-01Acknowledgements: We would like to thank KAUST for financial support. We thank R. Djebbi and U. bin Waheed for many useful discussions. We are also grateful to the associate editor, A. Stovas and two anonymous reviewers for their critical and helpful review of the paper.