Depth migration by reverse time migration requires the knowledge of a smooth approximation to the seismic velocity field. This background velocity model can be estimated by wave equation migration velocity analysis (WEMVA), an automatic process based on minimizing the errors in the kinematics of the depth migrated image. In this paper we present a WEMVA method where we use a combination of semblance and differential semblance to measure the errors in the positioning of reverse time migrated images. The errors are then turned into velocity updates by a gradient based optimization scheme. We apply the method to a 2D line extracted from a 3D marine survey acquired over the Snorre field in the North Sea. The resulting WEMVA velocities obtained from the field data are compared to the background velocities obtained by traveltime tomography, and also to well logs.


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