The subseafloor structure offshore western Canada wasimaged using first-order water-layer multiples from oceanbottomseismometer OBS data and the results were comparedto conventional imaging using primary reflections.This multiple-migration mirror-imaging method uses thedowngoing pressure wavefield just above the seafloor, whichis devoid of any primary reflections but consists of receiversideghosts of these primary reflections. The mirror-imagingmethod employs a primaries-only Kirchhoff prestack depthmigration algorithm to image the receiver ghosts. The additionaltravel path of the multiples through the water layer isaccounted for by a simple manipulation of the velocity modeland processing datum: the receivers lie not on the seabed buton a sea surface twice as high as the true water column. Migrationresults show that the multiple-migrated image providesa much broader illumination of the subsurface than ispossible for conventional imaging using the primaries, especiallyfor the very shallow reflections and sparse OBS spacing.The resulting image from mirror imaging has illuminationcomparable to the vertical incidence surface streamersingle-channel reflection data.
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