Abstract: A traveltime interpolation wavefront tracing method for numerical modeling of seismic wave in complex media is developed.It is based on an earth model consisting of uniform-velocity rectangular or polygonal cells with nodes placed at vertices and along cell edges.The wavefronts are propagated away from source throughout the entire model and sampled at the nodes,in which the first arrival time at a node is calculated by the interpolation of two previously computed traveltimes at all pair of adjacent nodes within a cell and minimization of traveltimes in the light of Fermat's principle. Once the wavefront traveltimes are sampled throughout the model, the minimal traveltime and raypaths from the source to receivers are easily obtained using the same technique as above.This method is regardless of model complexity,cell's shape and the positions of source and receivers.It can model all types of first arrival wave,such as direct waves,critical refractions and diffractions,and can trace entirely minimum traveltime paths.So it has a good flexibility and a high precision.At last,the method is applied to first arrival wave modeling of some typical near-surface models,the wavefront shapes and raypaths of which are shown explicitly.

Key words: seismic first break, wavefronts, ray paths, traveltime interpolation