| Gaussian beam migration method is the improvement and development of theKirchhoff migration method. It shows us flexibility and high-efficiency and can getsimilar results compared with wave equation migration methods. However,migration formulas of Gaussian beam migration are most given in frequency domainwhere it is diiffcult to compute the Green function. So it is necessary to improve thismigration method.To counter the problems above and based on the works of predecessors, in thispaper we exchange the order of integration in the migration formula to moving it fromthe frequency domain into the time domain. What’s more, we have derived a series of3D Gaussian beam prestack depth migration formulas which can be applied incommon-shot gathers, common-receiver gathers, common-offset gather, andcommon-midpoint gathers. After applied these migration formulas, the process ofcomputing Green functions can be simplified, we only need to acquire complextraveltime and amplitude of imaging points. For the reason that the migrationformulas of Gaussian beam in time domain are derived from the frequency domain,our methods are more efficient and can achieve the same migration results with thefrequency domain.In this paper, we also derive the formula to compute the complex traveltime ofgrid points by second order Tailor expansion, which is necessary to Gaussian beammigrationin time domain. In addition，the efficiency analysis and comparison of localplane wave decomposition are given in the paper.To verify the validity and effect of the new method, we employ a series oftheories and complex numerical models to m^e the test. The complex numericalmodels contain M^mousi data set, Sigsbee data set，BP data set, and actual deep-water data. Compared the imaging results of Gaussian beam migration in timedomain with that of Kirchhoff migration, conclusions can be drew that our methodcan achieve better migration results, especially for steep dip geologic body andregions under the high speed geologic body. |
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