Kirchhoff-type prestack depth migration is the methodmost popular for outputting offset gathers for velocitymodelupdating because of its flexibility and efficiency.However, conventional implementations of Kirchhoffmigration use only single arrivals. This limits its ability toimage complex structures such as subsalt areas. We use thebeam methodology to develop a multiarrival Kirchhoff beammigration. The theory and algorithm of our beam migrationare analogs to Gaussian beam migration, but we focus onattaining kinematic accuracy and implementation efficiency.The input wavefield of every common offset panel isdecomposed into local plane waves at beam centers on theacquisition surface by local slant stacking. Each plane wavecontributes a potential single-arrival in Kirchhoff migration.In this way, our method is able to handle multiarrivalscaused by model complexity and, therefore, to overcome thelimitation of conventional single-arrival Kirchhoff migration.The choice of the width of the beam is critical to theimplementation of beam migration. We provide a formulafor optimal beam width that achieves both accuracy andefficiency when the velocity model is reasonably smooth.The resulting structural imaging in subsalt and other structurallycomplex areas is of better quality than that fromsingle-arrival Kirchhoff migration.
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