TRAVEL-TIME AND AMPLITUDE ESTIMATION USING WAVE-FRONT CONSTRUCTION

We have developed and implemented a new method for estimating travelti mes and amplitudes in a general smooth two-dimensional (2-D) model. Th e basic idea of this wavefront (WF) construction approach is to use ra y tracing to estimate a new WF from the old one. The WF is defined as a curve (in 2-D) of constant traveltime from the source. The ray direc tion and amplitude will then be a function of s, the distance along th e front. To maintain a sufficiently small sampling distance along the WF, it is scanned at every time step and new rays are interpolated whe never the distance between two rays becomes larger than a predefined l imit. As the wavefronts are constructed. the data (i.e. traveltimes, a mplitude coefficients, etc.) are transferred to the receivers by inter polation within the ray cells. Advantages of the WF construction metho d are its flexibility, robustness, and accuracy. First, second. and la ter arrivals may be found at any point in the model. Any shape of the initial wavefront is possible. The drawbacks of the method are the sam e as for conventional ray tracing: large velocity contrasts, caustics and near-critical incidence angle of rays onto interfaces will give le ss accurate solutions.