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 traveltimes was modified to handle large, sharp velocity contrasts properly. The modified algorithm is faster and more accurate than several alternative schemes, and was incorporated in a procedure to compute reflection traveltimes. Snell's law for reflections is used in the vicinity of the reflecting interface. The reflector model is allowed to vary smoothly in depth, increasing the accuracy compared with a discretized reflector model. Reflection traveltimes are computed simultaneously for ail receivers, requiring only two applications of the finite-difference algorithm for each shot. This results in a significant saving in computation time in comparison with other algorithms which require one pass of the finite-difference algorithm for each shot and each receiver. The reflection traveltime procedure is well suited for incorporation in inversion schemes for 3-D velocity and reflector structure.