# Inspiration for Seismic Diffraction Modelling, Separation, and Velocity in Depth Imaging
## 1 Introduction  
Seismic diffraction events are produced because of small-scale elements in the subsurface, such as faults, fractures, channels, and rough edges of salt bodies; or because of small changes in the seismic reflectivity, such as those produced by fluid occurrence or fluid movement in the period of production. These diffracted waves contain the most important information for subsurface discontinuities [1]. The diffraction theory sometimes makes it impossible to understand the qualitative properties of diffraction phenomena [2]. Further, these diffraction data are also used for travel time approximation for anisotropic imaging [3]. The separation of diffraction is widely used [4; 5; 6; 7] for enhancement of seismic imaging, such as fault, fracture, complex variable velocity structure, and karstification imaging [8]. Further, the diffraction response for a nonzero separation of the source and receiver was presented by [PERSON] in 1977 [9], in which theoretical support was obtained for applying the zero-separation theory to stack the seismic data. Amplitude preservation of seismic waves was achieved by [PERSON] in1975 [10] by using the front sweep velocity approach, in which a graphical method evolves. The last decade was devoted to theoretical work and many methods were introduced, however the lack of implementation in the real world was limited due to computing power and facilities. In this decade, the computation increased drastically and the technology development increased compared to the last decade. Diffraction enhancement in prestack seismic data was introduced by [PERSON] in 2005 [11]. He introduced the most effective techniques, which involve the decomposition of seismic gather data into eigensections and flows based on radon transformations. Diffraction imaging using the multifocusing method was used in 2009 by [PERSON] [12], in which the diffraction focusing stack (DMFS) was used to separate the diffraction energy in a stack section and defocus the reflection energy over a large area. Diffraction separation has been widely used by [PERSON] since 2002 [13] using the Claerbout principle [14], and has contributed to the field of seismic diffraction imaging. Diffraction hyperbolic patterns occur frequently in seismic sections, and their existence is usually taken as evidence of abrupt discontinuities in the subsurface reflector geometry [10]. Geophysicists understand ray path geometry; for every \"point\" diffractor, the edge of the reflector and fault give rise to a hyperbolic pattern in a zero-offset section [9]. In an inclined case, a series of diffractions are originated along the fault surface so that the apex of each curve is on the fault plane. A conventional processing workflow suppresses the diffractions and enhances the reflections. Diffracted and reflected seismic waves are fundamentally different physical phenomena [15]. As shown in Figure 1, the source and receiver are on the surface. Once they are active, the reflections are recorded on a continuous reflector and a diffraction hyperbola is produced at the edges. This is because of the lateral acoustic impedance contrast. Further diffraction hyperbolas have positive to negative amplitudes, which generally decrease with time. The common practice during processing is that reflected waves are tuned and diffracted waves are suppressed by being considered as noise, but these diffracted events carry the most important information about the subsurface. The separation of seismic diffraction is not an innovative idea. A previous study [17] used diffraction to estimate the velocity from forward modeling and the local slant stack. Another study [18] used a common diffraction point section for imaging of diffraction energy and detection of local heterogeneities, while another study [19] simulated diffraction responses to enhance the velocity analysis. In this paper, we have developed a unique approach by integrating the previous solutions used for multiple eliminations.