From: Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept
Category 1
Category 2
Category 3
Category 4
Category 5
Peak freq. (Hz)
0.2–1.0
1.0–2.0
2.0–5.0
5.0–10.0
10.0–20.0
Numbers
15
17
21
20
14
Δ
0.06
0.03
0.013
0.006
0.003