Abstract：With the aid of finite-difference computation,the prestack depth migration by wave equation-based focus-point controlled illumination takes the influence of the medium parameters as velocity and density into matrix equations computed by finite-difference approach,which can be automatically adapted for any changes of velocity field,and the usage of fast Fourier transform can also fasten the computational speed of the wave field continuation.Therefore,the method has superiorities of both finite-difference migration and Fourier migration,and of both being adapted for severe variation of velocity field and guaranteeing the imaging effects of steep dip strata,which is one of effective imaging method for complex structure.The imaging steps for single focus point and surroundings are as follows: using finite-difference method of diffraction travel time to compute the synthetic operator in rectangle grid; ②using synthetic operator to synthesize plane source and plane wave records; ③the Fourier finite-difference wave equation prestack depth migration is implemented by synthetic plane source and plane wave records,obtaining the imaging results of focus point and surroundings.According to abovementioned imaging steps,the continuation of source wavefield and shot-gather records is implemented according to relevant extrapolation formula and finally using imaging conditions to compute imaging value.Selecting multiple focus points at geologic targets,the target-oriented controlled illumination migration imaging can be gained,and selecting multiple focus points on multiple horizons to carry out controlled illumination prestack depth migration can result in imaging in whole area.The approach achieved good effect by the test of Marmousi model.
