Fig. 3

Multiple ScS waveforms (a, d), amplitude spectra (b, e), and stacked spectral ratios (c, f) at OJ13 (a–c) and HNR (d–f) stations. In (a, d), the dotted curves denote the noise waveforms before arrivals of the multiple ScS waves. In (b, e), spectra of ScS_n and sScS_n are indicated by red curves and those of ScS_n+1 and sScS_n+1 by blue curves, those of noises are by dotted curves. In (c, f), the logarithm of the amplitude (left) and the phase (right) of the stacked spectral ratio are shown, respectively. Errors are estimated from noise spectra. A line fitting technique gives 331 ± 58 at OJ13 and 165 ± 54 at HNR