£W9 Wavefront Construction (WF) Ray Tracing in Tetrahedral Models — Application to 3-D Traveltime and Ray

Wavefront construction (WF) ray tracing in tetrahedral models-Application to 3-D traveltime and ray path computations Zhaobo Meng and Norman Bleistein Center for Wave Phenomena Colorado School of Mines For the purpose of building a fast and accurate tool for the computation of traveltimes and ray paths for 3-D depth imaging, we combine the techniques of tetrahedral model representation and 3-D wavefront construction (WF) ray tracing. The scheme is robust and efficient in the presence of complex earth structures. To efficiently represent a 3-D complex earth structure, a 3-D tetrahedral model as well as an auxiliary Cartesian cubic grid is used. In each layer, the "sloth " (the square of the slowness) is required to vary continuously, and specifically, in each cell, the sloth gradient is constant. The layers are separated by smoothly varying horizons. The tetrahedral model representation is based on the triangulation of the smooth horizons. WF ray tracing is used in the scheme. In WF ray tracing, rays are traced step-wise in traveltime through the model and are maintained by a triangular net-work, (i) to form the wavefront at each traveltime step, (ii) to evaluate quantities, such as traveltimes and ray paths at the receivers, and (iii) to interpolate new rays, whenever certain criteria are met. The quantities, such as traveltimes and ray paths, evaluated on a Cartesian cubic grid, are useful for depth imaging. For our kinematic ray tracing, which gives correct traveltimes and ray paths, an efficient alternative for dealing with caustics is presented. Key words: Tetrahedral model representation, WF ray tracing, traveltime and ray path computation