Iterative linearized migration and inversion

The objective of seismic imaging is to obtain an image of the subsurface reflectors, which is very important for estimating whether a reservoir is beneficial for oil/gas exploration or not. It can also provide the relative changes or absolute values of three elastic parameters: compressional wave velocity Vp, shear wave velocity Vs , and density ρ. Two ways can achieve the objectives. In approach I, the angle reflectivity is given by prestack depth/time migration or linearized inversion, and the relative changes of the three elastic parameters are estimated from the angle reflectivity by AVO/AVA inversion. In, approach II, the relative changes (by linearized inversion) or absolute values (by nonlinear waveform inversion) are obtained directly. I compare non-iterative linearized migration/inversion imaging, iterative linearized migration/inversion imaging, and non-linear waveform inversion. All of these imaging methods can be considered as back-projection and back-scattering imaging. From backscattering imaging, we know that seismic wave illumination has a key influence on so-called true-amplitude imaging, and I give an analysis for the possibility of relative true-amplitude imaging. I also analyze the factors that affect the imaging quality. Finally, I point out that the Born approximation is not a good approximation for linearized migration/inversion imaging, and that the De Wolf approximation is a better choice.