Fig. 8

2D section of the hybrid FD method second-step realization of the incident S-wave. Voluminal horizontal forces are applied at discrete sources placed at neighboring FD grid points—stars 1 and 2 belonging to the complete and scattered wave field, respectively. The scattered wave field is zero for replication test (see Figure 9) The excitation wave field bounding of the first step is pre-computed by the ray method; the second hybrid FD step is either the simple ray model structure (for replication test) or the Osaka basin structure. The inner and outer border lines placed at grid lines (on grid planes in 3D) are possible finite-extent realizations of the hybrid boundary. Vectors \(\overrightarrow{{s}_{s1}}\) and \(\overrightarrow{{s}_{s2}}\) are S-wave slowness vectors, \(\overrightarrow{{n}_{1}}\) is normal vector to the horizontal grid plane