We consider a case where full-azimuth reflection angle gathers were generated using a background VTI depth model. Residual moveouts (RMO) which were automatically picked on these 3D gathers along major horizons indicate considerable periodic azimuthal variations. Our aim is to use the azimuthally dependent RMOs to convert the background VTI model into interval orthorhombic layer parameters. Our method is based on a newly derived generalized Dix-based theory, assuming a locally varying 1D orthorhombic model, where at each location the vertical axis is the same for all layers but the azimuthal orientations are different. An effective model for such a layered structure represents a single layer with identical vertical time, effective compression vertical velocity, effective Thomsen parameters and an effective orientation. The NMO velocity and the surface offset azimuth of the effective model coincide with the parameters of the original package of layers for any azimuth of the phase velocity. Our approach starts with a Fourier-based conversion of the RMOs into azimuthally dependent NMO velocities, which are then inverted into three effective parameters. Finally, we apply the proposed generalized Dix-based inversion approach to estimate the interval orthorhombic parameters within each layer.


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