Abstract

The S‐wave Fourier amplitude spectra from the strong‐motion network data in the Himachal region of the northwest Himalaya are used to estimate site amplification and S‐wave attenuation (Qβ). For this analysis, 60 three‐component records were used from eight earthquakes with magnitudes ranging from M 3.4 to 5.4, recorded at 13 stations over a hypocentral distance range of R=9–48 km. The characteristics of the site amplification are analyzed using horizontal‐to‐vertical (H/V) Fourier spectral ratios of the S phase of the time history. The average amplification is close to unity except in a narrow frequency range of 2–4 Hz. The overall behavior of the H/V ratio is consistent with local geological conditions of the study region. The S‐wave quality factor Q(f  ) is estimated as 103f  0.66 for 0.2≤f≤20  Hz, and the validity is checked by computing path attenuation functions derived from the new Q(f  ). The estimated Q(f  ) is also compared with results from previous studies of Q for the Himalayan region.

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