To evaluate the site response using both empirical approaches (e.g. standard spectral ratio, ground motion models (GMMs), generalized inversion techniques, etc.) and numerical 1-D/2-D analyses, the definition of the reference motion, that is the ground motion recorded at stations unaffected by site-effects due to topographic, stratigraphic or basin effects, is needed. The main objective of this work is to define a robust strategy to identify the seismic stations that can be considered as reference rock sites, using six proxies for the site response: three proxies are related to the analysis of geophysical and seismological data (the repeatable site term from the residual analysis, the resonance frequencies from horizontal-to-vertical spectral ratios on noise or earthquake signals, the average shear wave velocity in the first 30 m); the remaining ones concern geomorphological and installation features (outcropping rocks or stiff soils, flat topography and absence of interaction with structures). We introduce a weighting scheme to take into account the availability and the quality of the site information, as well as the fulfillment of the criterion associated to each proxy. We also introduce a hierarchical index, to take into account the relevance of the proposed proxies in the description of the site effects, and an acceptance threshold for reference rock sites identification. The procedure is applied on a very large data set, composed by accelerometric and velocimetric waveforms, recorded in Central Italy in the period 2008–2018. This data set is composed by more than 30 000 waveforms relative to 450 earthquakes in the magnitude range 3.2–6.5 and recorded by more than 450 stations. A total of 36 out of 133 candidate stations are identified as reference sites: the majority of them are installed on rock with flat topography, but this condition is not sufficient to guarantee the absence of amplifications, especially at high frequencies. Seismological analyses are necessary to exclude stations affected by resonances. We test the impact of using these sites by calibrating a GMMs. The results show that for reference rock sites the median predictions are reduced down to about 45 per cent at short periods in comparison to the generic rock motions.

中文翻译：

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确定中高地震活动地区参考岩石地点的方法：在意大利中部的应用

为了使用两种经验方法（例如标准频谱比，地面运动模型（GMM），广义反演技术等）和数值1-D / 2-D分析来评估场地响应，参考运动的定义即需要在不受地形，地层或盆地影响的站点效应影响的站点上记录地面运动。这项工作的主要目的是使用六个代表现场响应的代理，定义一种可靠的策略来识别可以视为参考岩石站点的地震台站：三个代表与地球物理和地震数据分析（可重复站点）相关。残差分析项，噪声或地震信号在水平与垂直频谱比上的共振频率，前30 m的平均剪切波速度）；其余的涉及地貌和安装特征（露出岩石或坚硬的土壤，平坦的地形以及与建筑物之间没有相互作用）。我们引入一种加权方案，以考虑站点信息的可用性和质量以及与每个代理相关联的标准的实现。我们还引入了层次结构索引，以在站点影响的描述中考虑拟议代理的相关性，以及参考岩石站点识别的可接受阈值。该程序应用于由加速度计和测速波形组成的非常大的数据集，该数据集记录于2008-2018年期间在意大利中部。该数据集由3万多个波形组成，相对于在3.2-6级范围内的450次地震。5个，由450多个电台记录。在133个候选站中，总共有36个被确定为参考站：大多数安装在地形平坦的岩石上，但是这种条件不足以保证没有放大，特别是在高频下。进行地震分析以排除受共振影响的台站是必要的。我们通过校准GMM来测试使用这些网站的影响。结果表明，与普通岩石运动相比，参考岩石场地的中位预测值在短期内降低至约45％。特别是在高频下。进行地震分析以排除受共振影响的台站是必要的。我们通过校准GMM来测试使用这些网站的影响。结果表明，与普通岩石运动相比，参考岩石场地的中位预测值在短期内降低至约45％。特别是在高频下。进行地震分析以排除受共振影响的台站是必要的。我们通过校准GMM来测试使用这些网站的影响。结果表明，与普通岩石运动相比，参考岩石场地的中位预测值在短期内降低至约45％。