Fig. 6

Cross-correlation functions as a function of interstation distances filtered at 20–30 s, 10–20 s, and 5–10 s. The amplitudes are multiplied by \(\displaystyle \sum _k w^k_{ij}(f)\) in the frequency domain to produce similar noise levels for different pairs of stations. The dashed pink line shows the group velocity of each specified mode at a typical period for the 1-D isotropic model. The modes include the fundamental mode and first-higher-mode Rayleigh waves, 0 S, and 1 S. The TT components show wave packets of Love waves xT, which could not be identified as a single mode due to possible interference between the fundamental mode and the higher mode with very similar group and phase velocities. Taken from Takeo et al. (2016)