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The results of Chapter 5 demonstrate the benefits of combining P-wave data with reflection moveout of shear or mode-converted waves in parameter estimation for TI media. The advantages of multicomponent velocity analysis are even more crucial for lower-symmetry models described by a larger number of independent anisotropy parameters. This chapter is focused on moveout inversion of wide-azimuth, multi-component data from layered orthorhombic (sections 6.1-6.3) and monoclinic (section 6.4) media.

Velocity model building using PP and PS traveltimes is especially attractive because it does not require shear-wave excitation. We begin the first section by reviewing the properties of reflection moveout of converted waves for models composed of horizontal layers with a horizontal symmetry plane. As demonstrated in Chapter 1, PS traveltimes for such media are reciprocal with respect to the source and receiver positions and can be described by the conventional t2(x2) series. Furthermore, there exists a simple relationship between the NMO ellipses of pure and converted waves which, combined with the generalized Dix differentiation, makes it possible to compute the interval NMO ellipses of the split shear waves S1S1 and S2S2 from PP and PS (PS1 and PS2) data. Then the interval PP- and SS-wave NMO ellipses are inverted for the parameters of orthorhombic or monoclinic layers. This algorithm is tested on multicomponent (PP and PS) physical-modeling data acquired in several azimuthal directions over a block of orthorhombic composite material. The computed symmetry-plane NMO velocities of PP- and SS-waves are combined with the known reflector depth to estimate eight.

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