ABSTRACT

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 (Q_c), intrinsic attenuation parameter (Q_i), and scattering attenuation parameter (Q_s), 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 Q_c, Q_i, and Q_s 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 ($\mathrm{Q}={\mathrm{Q}}_0{\mathrm{f}}^{\eta }$) estimated for both regions are ${\mathrm{Q}}_{\mathrm{c}}=158{\mathrm{f}}^{1.18}$and ${\mathrm{Q}}_{\mathrm{c}}=194{\mathrm{f}}^{1.2}$, 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, Q_c values are found close to Q_s 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 (f_peak) 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.

摘要

本研究旨在估计印度中部喜马拉雅地区关于各种强运动参数如 Kappa 值 ( κ) 和场地效应。我们试图详细阐述区域结构异质性及其对研究区域地震危险性评估的影响。印度中部喜马拉雅地区的 50 个台站共记录了 81 次地震。特别关注 Kappa 值，该值显示从 0.03 s 到 0.095 s 的变化，推断在具有深层沉积物堆积的平原中获得的较高值证明了高频能量耗散，而硬土/岩石场地相应地表现出相对有限的衰减。为了证实这些结果，各种衰减参数，例如尾波品质因数 (Q _c )、固有衰减参数 (Q _i ) 和散射衰减参数 (Q _s)，已使用单一反向散射模型和 Wennerberg 公式对印度中央地震间隙喜马拉雅地区的两个区域进行了估计。_{发现 Q c}、 Q _i和 Q _s的估计值高度依赖于两个区域 1.5-24 Hz 频率范围内的频率。平均频率相关关系 ($\mathrm{问}={\mathrm{问}}_0{\mathrm{F}}^{\eta }$) 估计这两个地区是${\mathrm{问}}_{\mathrm{C}}=158{\mathrm{F}}^{1.18}$和 ${\mathrm{问}}_{\mathrm{C}}=194{\mathrm{F}}^{1.2}$， 分别。Q ₀值较低表明该地区具有高度的异质性，而η值较高表明该地区地震活动性较高。还发现固有衰减比散射衰减占主导地位，设想波衰减的行为通过在浅深度的花岗岩层内的吸收而​​发生。在较低频率下，Q _c值接近 Q _s值，这与理论测量结果一致，表明该区域下方存在复杂的地壳非均质性，影响地震波的传播，通过散射经历相当大的能量衰减。为了确认台站的总衰减，还确定了站点特征以检查放大的行为，因为地面运动由源、路径和站点的综合影响组成。这些位点以主要频率放大（f_峰值) 中部喜马拉雅地区的频率在 1.5 到 10 Hz 之间。不同的衰减和放大参数，如 kappa、Q 和场地效应，可用于该地区的详细地震危险分析（基于地震动预测方程），因为从社会经济的角度来看，该地区非常重要。