Large and complex velocity models, the prohibitive cost of depth imaging calculations, limited resources for interpreting velocity errors, and huge data sets: these are the obstacles that impede implementation of 3-D migration velocity analysis techniques. We have implemented a tomographic procedure that addresses these difficulties. It incorporates a flexible model parameterization, sparse ray tracing for traveltime approximations, automatic detection of residual moveout, parallel algorithm design, and a new feature: image computation in the direction normal to reflectors.

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