Abstract
Abstract Despite its unique properties the diffracted seismic wavefield is still rarely exploited in common practice. Although the first works on seismic diffraction date back at least as far as the 1950s, a first rigorous theoretical framework for diffraction imaging only evolved decades later and many important questions still remain unanswered until the present day. While this comparably slow progression can partly be explained by the lack of densely sampled high quality recordings, recent advances in acquisition and dedicated processing suggest we might be at the door step to a paradigm shift in which seismic diffraction could play an important role. Despite the fact that most major progress—in terms of data acquisition and processing—has been achieved for the reflected wavefield, upon closer inspection it becomes obvious that the concept of diffraction is deeply ingrained in migration-type seismic imaging. With the aim of complementing existing contributions on the topic, this chapter is an attempt to provide an intuitive introduction to the process of seismic diffraction. Discussed are the deep conceptual roots in optics, physical links to the Kirchhoff integral as well as diffraction types and their importance in different contexts of application. By means of controlled synthetic and academic as well as industry-scale field data examples, I suggest a simple integrated framework for noninvasive diffraction separation and high-resolution imaging, which remains computationally affordable and can be reproduced by the reader. Different applications suggest that the faint diffracted background wavefield is surprisingly rich and, once it is given a voice, it announces highly resolved features such as faults, fractures, and erosional unconformities, which remain notoriously hard to image conventionally. Extending the dominant theme of high-resolution seismic imaging, I illustrate how the superior illumination due to the uniform radiation of diffraction carries the additional potential for drastically reduced acquisitions and discuss the possibility of a systematic extraction of inter-scatterer traveltimes from coda waves.
Highlights
The first accounts on seismic diffraction date at least back to the 1950s, where the concept was recognized to form a very useful and important ingredient in initial attempts at migration (Hagedoorn, 1954)
The first works on seismic diffraction date back at least as far as the 1950s, a first rigorous theoretical framework for diffraction imaging only evolved decades later and many important questions still remain unanswered until the present day
When the field of optics is concerned, it becomes apparent that a rigorous theoretical framework for the treatment of diffraction phenomena is even of significantly older origin and can be traced back to the pioneering works of Grimaldi, Huygens, Babinet, Fresnel and Kirchhoff
Summary
The first accounts on seismic diffraction date at least back to the 1950s, where the concept was recognized to form a very useful and important ingredient in initial attempts at migration (Hagedoorn, 1954). The discussed multi-dimensional coherence analysis, which can be expressed by a very similar mathematical construct, is based on an adaptive and flexible traveltime kernel (equation 5) that is likewise suited to describe diffracted and reflected contributions While the former, even when formulated in the time domain, is in need of detailed knowledge of a velocity field for computing diffraction traveltimes, the latter in turn can facilitate the estimation of velocity structure from the estimated wavefront attributes (Duveneck, 2004; Bauer et al, 2017). Due to the fact that the N-th root semblance (equation 9), just like its conventional linear counterpart, is a normalized quantity, amplitude-strong features, connected to significant impedance contrasts appear well-resolved and bright as, for example, the stair steps of the velocity grid, which are the cause of extremely faint signals that can barely be recognized on individual traces (Meyer, 1934; Heincke et al, 2006; Schwarz, 2019).
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