Standard spectral ratio (SSR) technique has limited applicability in the estimation of spectral amplification in the vast Indo-Gangetic plains (IGP). Here we take recourse to an alternative approach using the recordings of three largest aftershocks of the 2015 Gorkha earthquake (M_w 7.9). We separately compute geometric mean source spectrum of an event from the recordings at hard sites in India and from the target IGP site. The ratio of the source spectrum from the target IGP site to the geometric mean source spectrum from the hard sites (denoted here, for brevity, as RSS) provides the desired spectral amplification. At four soft IGP sites where a comparison is possible, the spectral amplifications from RSS and SSR methods show a reasonable resemblance but also significant differences, owing to the difference in the definition of the reference spectrum. RSS method may be preferable if the input motion can only be prescribed at a generic hard site. We document amplification at 28 IGP sites using the RSS technique. The fundamental frequency, f₀, of the sites increase from 0.12 Hz near the foothills of Himalayas to 2.0 Hz at the southern edge of the basin and the amplification reaches about 10. At several sites, f₀ is difficult to select and the amplification of ~5 is broadband in the range 0.12–0.7 Hz. Application of SSR technique to teleseismic S-wave data recorded in the IGP reveals that this approach may be useful in the estimation of amplification at low frequencies (f < 0.5 Hz).

中文翻译：

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根据印度软硬地源频谱比估算印度中部恒河平原中部的地震波放大率

标准光谱比（SSR）技术在广阔的印度恒河平原（IGP）的光谱放大率估算中具有有限的适用性。在这里，我们采用另一种方法，即使用2015年戈尔卡地震（M _w7.9）。我们分别从印度硬站点的记录和目标IGP站点分别计算事件的几何平均源谱。来自目标IGP站点的源频谱与来自硬站点的几何平均源频谱（此处为简洁起见，以RSS表示）的比率提供了所需的频谱放大。在四个可能进行比较的软IGP站点上，由于参考频谱定义的差异，RSS和SSR方法的频谱放大显示出合理的相似性，但也存在显着差异。如果只能在通用硬站点上规定输入运动，则最好使用RSS方法。我们使用RSS技术记录了28个IGP站点的扩增。基本频率f ₀的站点从喜马拉雅山山麓附近的0.12 Hz增加到盆地南部边缘的2.0 Hz，并且放大率达到10。在几个站点，f ₀很难选择，〜5的放大率是宽带的。范围0.12–0.7 Hz。将SSR技术应用于在IGP中记录的远震S波数据表明，该方法可用于估算低频（f  <0.5 Hz）的放大率。