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Multiparametric traveltimes: Concepts and applications Dr. Martin Tygel (University of Campinas Campinas SP, Brazil)
Fecha , hrs
Lugar: Audiovisual de Ciencias de la Tierra
Ponente(s): Dr. Martin Tygel
University of Campinas Campinas SP, Brazil
 Traveltime stacking is one of the most fundamental tools in the processing of multicoverage seismic data. The most popular stacking traveltime is the normal moveout (NMO), upon which the celebrated common-midpoint (CMP) method is based. Established in the 1960s, the CMP method remains as an obligatory step in any seismic processing sequence.
The NMO stacking traveltime depends on a single parameter (the NMO velocity)and is performed on individual CMP gathers, thus depending on offset only. In spite of its well-recognized good properties, such as a valuable zero-offset (ZO) stacked section and an NMO-velocity field, NMO stacking can be seen to have two main drawbacks: The first one is that it employs only a fraction (CMP gathers) of the multicoverage data and, as a consequence, takes no advantage of the redundancy contained in the full data. The second one is the fact that it delivers a single parameter (NMO velocity), not much information extraction from the huge and costly seismic data.

In the 1980s, in response to the demands of seismic processing in anisotropic media, multiparametric nonhyperbolic moveouts came into play. Still dependent on offset only, such moveouts mainly were applied to transverse anisotropic media with a vertical axis of symmetry.
Moveout extensions for more complex anisotropic media are available in recent literature, being a topic of active ongoing research.

A vigorous attempt to overcome the limitations of offset dependent moveouts came about in the late 1990s by the introduction of multiparametric moveouts depending on both midpoint and offset coordinates and also fully in 3D. Moreover, the parameters introduced in the new traveltimes were seen to be very useful for other imaging purposes, such as, e.g., time migration, separation of reflections and diffractions, time-to-depth conversion, tomography and, more recently, data regularization.

In this lecture, I discuss the multiparametric traveltimes that are the most natural extensions of the classical single-parameter NMO and time-migration moveouts. More specifically, these are the 3D hyperbolic (second-order Taylor polynomial) mainly designed for reflections and double-square-root (sum of two hyperbolic moveouts), mainly designed for diffractions. Both traveltimes are defined for varying midpoint and half-offset coordinates.

Besides a brief discussion of the traveltime expressions and interpretation of their parameters, various applications on the above-mentioned topics are presented. Finally, perspectives and actual challenges of the multiparametric traveltime approach to seismic imaging are commented.

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