Slowness-driven Gaussian-beam prestack depthmigration for low-fold seismic data

摘要

Subsurface images based on low-fold seismic reflectiondata or data with geometry acquisition limitations, such asobtained from ocean-bottom seismography OBS, are oftencorrupted by migration swing artifacts. Incorporatingprestack instantaneous slowness information into the imagingcondition can significantly reduce these migration swingartifacts and improve image quality, especially for areas withpoor illumination. We combine the horizontal surface slownessinformation of observed seismic data with Gaussianbeamdepth migration to implement a new slowness-drivenGaussian-beam prestack depth migration whereby Fresnelweighting is combined naturally with beam summation. Theprestack instantaneous slowness information is extractedfrom the original OBS or shot gathers using local slant stacksand is combined with a local semblance analysis. During migration,we propagate the seismic energy downward, knowingits instantaneous slowness information.At each image location,the beam summation is localized in a resolution-dependentFresnel zone; the instantaneous slowness informationcontrols the beam summation. Synthetic and real data examplesconfirm that slowness-driven Gaussian-beammigration can suppress most noise from inadequate stackingand give a clearer migration result.