FINITE-DIFFERENCE SOLUTION OF THE EIKONAL EQUATION USING AN EFFICIENT, 1ST-ARRIVAL, WAVE-FRONT TRACKING SCHEME

First-break traveltimes can be accurately computed by the finite-diffe rence solution of the eikonal equation using a new comer-node discreti zation scheme. It offers accuracy advantages over the traditional cell -centered node scheme. A substantial efficiency improvement is achieve d by the incorporation of a wavefront tracking algorithm based on the construction of a minimum traveltime tree. For the traditional discret ization scheme, an accurate average value for the local squared slowne ss is found to be crucial in stabilizing the numerical scheme for mode ls with large slowness contrasts. An improved method based on the trad itional discretization scheme can be used to calculate traveltimes in arbitrarily varying velocity models, but the method based on the comer -node discretization scheme provides a much better solution.