Fig. 3

Histograms showing the probability density functions of peak amplitude ratios for the four frequency bands: 0.5–1, 1–2, 2–4, and 4–8 Hz. Yellow histograms show the distributions of peak ratios when all JMA stations are considered. Red and blue histograms separate the peak ratio distributions into JMA ground surface and borehole stations, respectively. The former is showing mostly larger values, and both are greater than the reference numbers for the Hi-net stations. The grey bands indicate the peak ratio mean plus-and-minus one standard deviation for all Hi-net data according to Table 1 of Nishimura (2012)