TRAVEL-TIME AND AMPLITUDE ESTIMATION USING WAVE-FRONT CONSTRUCTION

We have developed and implemented a new method for estimating traveltimes and amplitudes in a general smooth two-dimensional (2-D) model. The basic idea of this wavefront (WF) construction approach is to use ray 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 direction and amplitude will then be a function of s, the distance along the front. To maintain a sufficiently small sampling distance along the WF, it is scanned at every time step and new rays are interpolated whenever the distance between two rays becomes larger than a predefined limit. As the wavefronts are constructed. the data (i.e. traveltimes, amplitude coefficients, etc.) are transferred to the receivers by interpolation within the ray cells. Advantages of the WF construction method are its flexibility, robustness, and accuracy. First, second. and later 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 same as for conventional ray tracing: large velocity contrasts, caustics and near-critical incidence angle of rays onto interfaces will give less accurate solutions.