Fig. 1

Example of (a, c) three-component seismograms and (b, d) amplitude spectral ratios in the S-coda time window observed for two S-net stations. Locations of the two S-net stations (a, b: N.S1N01, c, d: N.S6N14) are shown in Fig. 2a. Red rectangles are the S-coda time window used to compute the amplitude spectral ratios. Red, orange, and blue curves are the logarithmic averages of Y/X, X/U, and Y/U amplitude spectral ratios, respectively. Dotted red curves are the logarithmic standard deviation of the Y/X amplitude spectral ratios