Abstract We estimated the spectral decay parameter, kappa (κ) for the Northwest (NW) Himalaya and the Northeast (NE) Himalaya, particularly NE India, using the strong motion records obtained from accelerographs installed in these regions. We estimated κ from the horizontal as well as vertical records from 294 accelerograms (three components). It has been observed that in the NW Himalaya and NE India, the value of κ varies considerably among different sites. This may be due to the lateral heterogeneity of the crust in these regions. The estimated values of κ for the NW Himalaya and the NE India region do not vary with magnitude, which shows that κ is independent of the earthquake size. It was observed that the value of κ is more for the horizontal components as compared to vertical in both the regions. The local site conditions and tectonic regime influence the value of κ as it was found that κ is more at sites covered by alluvium than at rock sites, in both the regions. The average value of κ of horizontal and vertical components for the NW Himalaya is 0.050 ± 0.009s and 0.048 ± 0.010s, respectively. For the NE India region, the average value of κ of horizontal and vertical components is 0.0368 ± 0.0054s and 0.0334 ± 0.0091s, respectively, indicating that geological formations in the NE region are more competent (compact) and less attenuative. The high values of kappa indicate that most of the high frequency energy will be removed during strong earthquakes in these regions. The kappa values estimated for both the regions may be helpful for attenuation studies and updating hazard maps in these regions.

中文翻译：

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西北和东北喜马拉雅地区近地表衰减参数 kappa (κ) 的估计

摘要我们使用从安装在这些地区的加速度计获得的强运动记录估计了西北（NW）喜马拉雅山和东北（NE）喜马拉雅山，特别是印度东北部的光谱衰减参数 kappa（κ）。我们从 294 个加速度图（三个分量）的水平和垂直记录估计 κ。据观察，在喜马拉雅西北部和印度东北部，不同地点的 κ 值差异很大。这可能是由于这些地区地壳的横向非均质性所致。NW喜马拉雅和NE印度地区的κ估计值不随震级变化，这表明κ与地震大小无关。据观察，与两个区域中的垂直分量相比，水平分量的 κ 值更大。当地的场地条件和构造制度会影响 κ 的值，因为我们发现，在这两个地区，被冲积层覆盖的地点的 κ 值高于岩石地点。NW喜马拉雅山水平和垂直分量κ的平均值分别为0.050±0.009s和0.048±0.010s。对于印度东北地区，水平和垂直分量 κ 的平均值分别为 0.0368±0.0054s 和 0.0334±0.0091s，表明 NE 地区的地质地层更胜任（致密）和更少的衰减。kappa 的高值表明在这些地区发生强烈地震时，大部分高频能量将被去除。为这两个区域估计的 kappa 值可能有助于衰减研究和更新这些区域的危险地图。