Processing converted-wave data in the tau-p domain: rotation toward the source and moveout correction

Raul Cova and Kris Innanen

ABSTRACT

The asymmetry of the converted-wave raypath is one of the main sources of complexity in the processing of multicomponent data. Such asymmetry is controlled by Snell's law, which also states that in an isotropic and flat layered medium the ray-parameter value p is preserved, even for converted-wave modes. In this study we propose processing converted-wave data in the ray-parameter domain as a more suitable framework for dealing with this type of waves. Here we address the problem of rotations toward the source in 2D media with dipping reflectors, converted-wave velocity analysis and NMO corrections. Results show that reversing the polarity of the traces to correct for the orientation of the horizontal components around the zero ray-parameter condition provides consistent polarities along all the events. Also, using an elliptical approximation to the PS-moveout in τ-p domain provides an alternative tool for velocity analysis and converted-wave moveout correction. Its implementation is very similar to the conventional processing in x-t domain. However, results show that in τ-p domain the information in shallow events can be fully exploited. The ability of shallow events to reach wider reflection angles, therefore larger ray-parameter values, makes them a good target for processing in τ-p domain. An accurate algorithm for the τ-p transformation is required to avoid introducing numerical artifacts. Here we noticed that the polarity reversals present in the converted-wave events are a new source of these artifacts. Efforts on developing a new τ-p algorithm able to account for these polarity reversals is needed to provide cleaner data for further processing.

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