3-D FINITE-DIFFERENCE REFLECTION TRAVEL-TIMES

A method has been developed to compute seismic reflection traveltimes in complex 3-D velocity models with complex 3-D reflector geometry. An existing finite-difference algorithm for calculating first-arrival tr aveltimes was modified to handle large, sharp velocity contrasts prope rly. The modified algorithm is faster and more accurate than several a lternative schemes, and was incorporated in a procedure to compute ref lection traveltimes. Snell's law for reflections is used in the vicini ty of the reflecting interface. The reflector model is allowed to vary smoothly in depth, increasing the accuracy compared with a discretize d reflector model. Reflection traveltimes are computed simultaneously for ail receivers, requiring only two applications of the finite-diffe rence algorithm for each shot. This results in a significant saving in computation time in comparison with other algorithms which require on e pass of the finite-difference algorithm for each shot and each recei ver. The reflection traveltime procedure is well suited for incorporat ion in inversion schemes for 3-D velocity and reflector structure.