Fig. 6

Results of the numerical simulation for isotropic media. a Sketch for model space with two isotropic layers with a flat interface at a depth of 2 km. b Auto-correlation functions (ACFs) as a function of polarization direction, calculated with the model in Fig. 6a. c Model for the two-dimensional (2D) experiment for calculating differential travel time between direct S and reflected S waves. Red dots indicate locations of sources. The triangle shows the location of the station. Gray shaded area corresponds to low-velocity sediment. The parameters on the velocity model are the same as those in Fig. 6a and Table 1. d Red dots represent differential travel times between direct S and reflected S waves for each source (Fig. 7a). The black solid line corresponds to the travel time of two-way S reflection with zero offset for the one-shot case. The gray shaded area indicates the approximate region for constructive interference when stacking reflected S waves. e ACFs as a function of angle from vertically downward. Each ACF was calculated by the wavefield for each source shown in Fig. 6c. f Same as Fig. 6e but the range of lag time for 3–5 s and the amplitude is described by colors. Red dots are the same as those in Fig. 6d but for 0° ≦ ϕ ≦ 45° (x ≧ 8 km)