ABSTRACT

We attempted a comprehensive site response study of Garhwal-Kumaun Himalaya in the Central seismic Gap (CSG) using the data collected from 97 strong motion, microtremor and broadband stations. Site response parameters such as predominant frequency (f_peak), site amplification (A_max) and average shear-wave velocity up to a depth of 30 m (V_S30) were estimated by adopting the Nakamura technique. Spatial maps of these parameters were prepared to show the distribution of site response functions across the region. The estimated parameters show a good correlation with site geology. Decreasing order of sediment thickness from foothills to Lesser Himalaya was observed in the region. The estimated V_S30 values were correlated with global V_S30 values as well as available field measurements and 1D velocity inversion results, it shows a good agreement. The sites were classified as per the NEHRP site classification scheme based on the V_S30 value. From this study, we inferred that the V_S30 values estimated from the Nakamura technique can be used as an alternate proxy for determining the average shear wave velocity up to a depth of 30 m in the absence of substantial field measurements due to challenging terrain conditions. Such results of site response analysis may be used for preliminary earthquake hazard assessment in the region.

摘要

我们尝试使用从 97 个强震台站、微震台站和宽带台站收集的数据对中央地震间隙 (CSG) 中的 Garhwal-Kumaun 喜马拉雅山进行全面的场地响应研究。采用 Nakamura 技术估计了主要频率 ( f _peak )、站点放大率 (A _max ) 和深度达 30 m (V _S30 ) 的平均剪切波速度等站点响应参数。准备这些参数的空间图以显示整个区域的站点响应函数的分布。估计的参数与现场地质情况有很好的相关性。在该地区观察到从山麓到小喜马拉雅的沉积物厚度递减顺序。估计 V _S30值与全球 V _S30值以及可用的现场测量和一维速度反演结果相关，显示出良好的一致性。_{这些站点根据基于 V S30}值的 NEHRP 站点分类方案进行分类。从这项研究中，我们推断，在由于具有挑战性的地形而没有大量现场测量的情况下，从 Nakamura 技术估计的 V _S30值可以用作确定深度达 30 m 的平均剪切波速度的替代代理条件。这样的场地反应分析结果可用于该地区的初步地震危险性评估。