A B S T R A C TA tomographic inversion method is presented that uses kinematic information in the form of zero-offset traveltimes and kinematic wavefield attributes (first and second spatial traveltime derivatives) to determine smooth, laterally inhomogeneous 3D subsurface velocity models for depth imaging. The kinematic wavefield attributes can be extracted from the seismic prestack data by means of the common reflection surface (CRS) stack. The input for the tomography is then taken from the resulting attribute volumes at a number of pick locations in the CRS stacked zero-offset volume. As a smooth model description based on B-splines is used and reflection points are treated independently of each other, only locally coherent events in the stacked volume are required and very few picks are needed. Thus, picking is considerably simplified.During the iterative inversion process, the required forward-modelled quantities are obtained by dynamic ray tracing along normal rays pertaining to the input data points. Fréchet derivatives for the tomographic matrix are calculated with ray perturbation theory. The inversion algorithm is demonstrated on a 3D synthetic data example, where the kinematic wavefield attributes have directly been obtained by forward modelling.
I N T R O D U C T I O NThe construction of velocity models is an essential step in the process of seismic depth imaging, particularly in the case of laterally inhomogeneous media. A commonly used tool for velocity model building in laterally inhomogeneous media is reflection tomography (e.g. Farra and Madariaga 1988;Stork and Clayton 1991). In reflection tomography, an optimum model is determined iteratively by calculating global model updates such that the misfit between traveltimes picked along reflection events in the seismic data and the corresponding values calculated in the model is minimized. The main drawback of conventional reflection tomography is the fact that for its application, picking of a large number of reflection traveltimes, usually along continuous horizons and across several