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Reflection traveltimes recorded over azimuthally anisotropic fractured media can provide valuable information for reservoir characterization. As recently shown by Grechka and Tsvankin, normal moveout (NMO) velocity of any pure (unconverted) mode depends on only three medium parameters and usually has an elliptical shape in the horizontal plane. Because of the limited information contained in the NMO ellipse of P-waves, it is advantageous to use moveout velocities of shear or converted modes in attempts to resolve the coefficients of realistic orthorhombic or lower-symmetry fractured models. Joint inversion of P and PS traveltimes is especially attractive because it does not require shear-wave excitation. Here, we show that for models composed of horizontal layers with a horizontal symmetry plane, the traveltime of converted waves is reciprocal with respect to the source and receiver positions (i.e., it remains the same if we interchange the source and receiver) and can be adequately described by NMO velocity on conventional-length spreads. The azimuthal dependence of converted-wave NMO velocity has the same form as for pure modes but requires the spatial derivatives of two-way traveltime for its determination. Using the generalized Dix equation of Grechka, Tsvankin, and Cohen, we derive a simple relationship between the NMO ellipses of pure and converted waves that provides a basis for obtaining shear-wave information from P and PS data. For orthorhombic models, the combination of the reflection traveltimes of the P-wave and two split PS-waves makes it possible to reconstruct the azimuthally dependent NMO velocities of the pure shear modes and to find the anisotropic parameters that cannot be determined from P-wave data alone. The method is applied to a physical modeling data set acquired over a block of orthorhombic material-Phenolite XX-324. The inversion of conventional-spread P and PS moveout data allowed us to obtain the orientation of the vertical symmetry planes and eight (out of nine) elastic parameters of the medium (the reflector depth was known). The remaining coefficient (c 12 or δ (3) in Tsvankin's notation) is found from the direct P-wave arrival in the horizontal plane. The inversion results accurately predict moveout curves of the pure S-waves and are in excellent agreement with direct measurements of the horizontal velocities.

This paper develops a new display technique for seismic cross‐sections, called spectral color. The need to visualize frequency information in seismic data is recognized uniformly and often is accomplished through the color display of instantaneous frequency. The spectral content of a reflected event can carry information about the reflecting horizon’s characteristics which will not be resolved in the instantaneous state of the record. Spectral color is devised to overcome the problem of displaying an entire localized spectrum at each time sample and offset of a seismic section. The localized spectrum is calculated with a relatively new time‐frequency representation called the S-transform, which combines a Fourier technique with adaptive windowing in the frequency domain. A color (RGB triplet) based on the localized spectral content is calculated and the pixel is displayed at the appropriate position in the seismic section. As a result, the seismic cross‐section is displayed in an intuitive manner that is much the way we see the world around us. Strongly reflecting or well‐lit objects appear to us as bright, and the color tells us about the frequency content of the reflected energy. Spectral color is applied to ultrasonic laboratory data acquired over a thin anisotropic disk. It reveals a change in color (spectral content) with azimuth where no significant amplitude variation with azimuth was observed. Spectral color is illustrated further by application to a 3-D field data set and is compared to other, more standard, color displays.

A system for area-beam energy-subtraction monochromatic radiography was developed and tested. It utilizes a bent Laue crystal monochromator developed at the National Synchrotron Light Source (NSLS), and a compact rotating anode X-ray source developed at the Science Research Laboratory (SRL). The K(alpha) characteristic lines (both K(alpha 1) and K(alpha 2) of the cerium and barium targets were diffracted by the monochromator and used for the above- and below-K-edge imaging, respectively, of phantoms with iodine contrast agents. Digital subtraction of the images produced an iodine image.

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