sfeikonal solves the eikonal equation using the Fast Marching Method. This computation produces first-arrival traveltimes on a fixed grid.

The following example from sep/fmeiko/fmarch shows traveltime contours for a point source inside the SEG/EAGE salt model.

The point source can be specified by its coordinates xshot=, yzhot=, and zshot= (note that the depth coordinate zshot corresponds to the first axis). In a small box around the source, the solution is computed analytically to avoid errors from the point-source singularity. The size of the box can be specified in samples (b1=, b2=, and b3=) or in physical dimensions (br1=, br2=, and br3=). For a plane-wave source instead of a point source, use plane1=y, plane2=y, or plane3=y. The plane is assumed to be aligned with the grid. For computing a traveltime table with multiple sources, the source coordinates can be specified in a file given by shotfile=. The order of accuracy in the finite-difference scheme is specified by order= parameter.

The following plot from sep/fmsec/cvel shows the error difference between the first- and second-order computations in a constant-velocity medium.

sfeikonal computes isotropic traveltimes. For an extension to VTI anisotropy, see sfeikonalvti.