CALCULATION OF THE SEISMIC 1ST-BREAK TIME FIELD AND ITS RAY PATH DISTRIBUTION USING A MINIMUM TRAVEL-TIME TREE ALGORITHM

A grid search method, analogous to Huygens' Principle, is employed to find the first-break seismic traveltime field in a seismic model. By defining a set of directions in space, a dynamic directed graph (digraph) containing the first-break time information can be constructed during the minimum traveltime tree-searching process. The dynamic di-graph has far fewer edges than the global graph suggested by previous researchers. An efficient sorting algorithm (heapsort) is adapted to the traveltime data structure by employing an indirect heap strategy. The computational speed can thus be improved several times over other approaches. The minimum traveltime tree algorithm is an efficient and flexible method to simultaneously calculate the first-break time field and the corresponding ray paths. It produces a robust and global result in comparison with traditional ray tracing methods. Later seismic phases can also be handled by imposing constraints on the ray paths. A subgrid technique is better than the normal grid technique in terms of accuracy and efficiency. The construction of the di-graph uses the local directional information of ray-paths and therefore local anisotropic information can be naturely incorporated. The first-break time field and its ray paths in an anisotropic model can be calculated as easily as those for an isotropic model.