ABSTRACT

Near- and postcritical spherical-wave reflections contain amplitude and phase variations with incident angle that are not predicted by plane-wave solutions. However, if a spherical wavefield is decomposed into plane waves by a time-intercept-slowness (τp) transform, then plane-wave reflection coefficients (the Zoeppritz) can be used as the basis of amplitude/phase versus angle analysis. The spherical-wave effects on reflection coefficients near the critical angle (in the time-offset domain) were decomposed by τp transformation into plane waves. Kinematic ray tracing linked the reflection angle at the target reflector and the apparent slowness at the surface receiver, which enabled extracting the amplitude/phase versus angle data at the reflector from the surface τp data. The most reliable inversion results were obtained by combining the extracted amplitudes and phases in a composite inversion for the elastic parameters below the target reflector.

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