Site Amplification and Frequency-Dependent Attenuation Coefficient at Rock Sites of the Himachal Region in Northwest Himalaya, India.

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 5-wave attenuation (Q_&bgr;). 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 5-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. [ABSTRACT FROM AUTHOR]