3-D SEISMIC-REFLECTION TOMOGRAPHY ON TOP OF THE GOCAD DEPTH MODELER

The estimation of velocity macro-models by seismic reflection tomograp hy is studied in three-dimensions. Inversion techniques based on the k inematics of seismic data require an appropriate parameterization of t he geological macro-model, in particular as far as the velocity field is concerned. The step toward structurally complex geological models i s achieved by exploiting a new approach to 3-D depth modeling: GOCAD. The peculiarities inherent to GOCAD triangulated surfaces and its asso ciated discrete smooth interpolator (DSI) have led to the development of original ray-tracing techniques. By exploiting intensively the topo logy of the triangulated surfaces, these new algorithms make it possib le to reach a good balance between accuracy and computation performanc e. To build a 3-D macro-model estimation tool, ray-tracing is then ass ociated with a least-squares inversion of depth parameters and velocit y parameters from 3-D zero-offset traveltimes and stacking velocities, or multi-offset prestack traveltimes from 2-D seismic lines.