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This study aims to estimate attenuation characteristics of the central Himalayan region of India concerning various strong-motion parameters such as Kappa value (κ) and site effects. We have tried to elaborate on the regional structural heterogeneities and their implications towards the seismic hazard assessment of the study region. A total of 81 earthquakes recorded at 50 stations situated in the central Himalayan region of India are used for the purpose. The particular focus is kept on Kappa value, which shows variability from 0.03 s to 0.095 s, inferring the higher values obtained in plains with deep sediment accumulations proving high-frequency energy dissipation and stiff-soil/rocky sites exhibit comparatively limited attenuation accordingly. To substantiate these results various attenuation parameters such as coda wave quality factor (Qc), intrinsic attenuation parameter (Qi), and scattering attenuation parameter (Qs), have been estimated for two regions in the central seismic gap Himalayan region of India employing the single backscattering model and Wennerberg formulation. The estimated values of Qc, Qi, and Qs are found to be highly dependent on frequency in the frequency range 1.5–24 Hz for both the regions. The average frequency-dependent relationships ( Q = Q 0 f η ) estimated for both regions are Q c = 158 f 1.18 and Q c = 194 f 1.2 , respectively. The low value of Q0 shows that the region is highly heterogeneous while the higher value of η indicates higher seismicity in the area. It is also found that intrinsic attenuation is predominant over the scattering attenuation, envisaging the behavior of the wave attenuation through the absorption within the granitic layer at shallow depths. At lower frequencies, Qc values are found close to Qs values, which is in agreement with the theoretical measurements suggesting the presence of complex crustal heterogeneities beneath the region affecting the propagation of seismic waves experiencing considerable decay of energy through scattering. To confirm the aggregate attenuation on the stations, the site characteristics are also determined for examining the behavior of the amplification as the ground motion is comprised of the combined effect of the source, path, and site. The sites are amplified at a predominant frequency (fpeak) in between 1.5 to 10 Hz for the central Himalayan region. The different attenuation and amplification parameters like kappa, Q, and site effects can be utilized for detailed seismic hazard analysis (based on ground motion prediction equations) of the area as this region is of great importance from a socio-economic point of view. [ABSTRACT FROM AUTHOR]

Site effect estimation using recorded ground motion is an effective approach to assess the seismic hazard of a region. Keeping the same thing in mind, an endeavor is being made to study the local site effects at different locations in the North East region of India through analysis of recorded strong ground motion data provided by Indian strong motion network. The data recorded at 25 sites from 37 earthquakes with a magnitude range M L 4.0–6.9 have been utilized. The estimated predominant frequencies ( f p e a k ) using horizontal to the vertical spectral ratio (HVSR) is well observed for various sites placed in various geological formations like the Precambrian, Tertiary and Quaternary Consequently, the pseudo velocity response (PSV) for 5% critical damping is estimated and compared with the regional geological formations, especially in the Brahmaputra Valley region. It is further noticed that the HVSR, as well as PSV, show a noticeable correlation according to the geological set up of the region for most of the sites, giving a clear idea about the site effect evaluation. Analyzed strong motion data also show the effect of non-linearity, which is an important parameter as it explains the inelastic behavior of the soil causing a reduced or non-linear amplification. Since some of the sites used in present work do not correlate with geology, the sites used for HVSR estimation are used to classify them according to the classical approach employing f p e a k . All the sites are classified in four different classes namely A, B, C, and D based on shear wave velocity in the upper 30 m. The outcome of the present study is being shown in the form of contour maps for f p e a k and site amplification for various types of buildings in order to assess the seismic hazard and risk mitigation. [ABSTRACT FROM AUTHOR]