Benjamin Schwarz 

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 non-invasive 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.