Abstract. This research uses a large dataset from the Italian Seismic Microzonation Database, containing nearly 15,000 measured shear wave velocity (Vs) profiles across Italy, to investigate the uncertainties in seismic risk assessment. This extensive collection allows a detailed study of the seismic properties of soil with unparalleled precision. Our focus is on evaluating Vs variations with depth within uniformly clustered areas, known as seismic microzones. These zones are carefully identified based on their spatial correlation and homogeneity in geological, geophysical, and geotechnical characteristics, which are critical for accurate prediction of seismic response. We contrast these results with clusters formed purely based on geographic survey density (here defined geographic clusters), thereby assessing the depth of our understanding of the subsurface geological and geophysical context. These results were further compared with those reported in the seismic code and literature. This study of depth-dependent Vs variations helps to refine our models of subsurface seismic behaviour. Our main discoveries show that: 1) uncertainties associated with seismic microzones (geological and geophysical clusters) are consistently lower than those identified in geographic clusters, particularly in the first 30 m of depth; 2) Vs profile variations show negligible increases in uncertainty within a certain range of correlation distances (up to about 4,500 m); 3) uncertainties for seismic microzones are lower than those previously reported in seismic codes and in the literature, indicating the effectiveness and precision of our methodological approach. The results of this study significantly improve local seismic response analysis and highlight the critical role of depth and spatial correlation in understanding seismic hazard. The dataset is available at https://doi.org/10.5281/zenodo.10885590 (Mori et al., 2024).

中文翻译：

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描述意大利地震微分区数据库中剪切波速度剖面的不确定性


摘要。本研究使用意大利地震微分区数据库中的大型数据集（包含意大利各地近 15,000 个测量的剪切波速度 (Vs) 剖面）来调查地震风险评估的不确定性。这个广泛的收藏可以以无与伦比的精度详细研究土壤的地震特性。我们的重点是评估均匀聚集区域（称为地震微区）内 Vs 随深度的变化。这些区域是根据地质、地球物理和岩土特征的空间相关性和均匀性仔细识别的，这对于准确预测地震响应至关重要。我们将这些结果与纯粹基于地理调查密度形成的聚类（此处定义为地理聚类）进行对比，从而评估我们对地下地质和地球物理背景的理解深度。这些结果进一步与地震规范和文献中报告的结果进行了比较。这项与深度相关的 Vs 变化的研究有助于完善我们的地下地震行为模型。我们的主要发现表明： 1) 与地震微区（地质和地球物理集群）相关的不确定性始终低于地理集群中确定的不确定性，特别是在深度的前 30 m 内； 2) Vs 剖面变化表明，在一定的相关距离范围内（最多约 4,500 m），不确定性的增加可以忽略不计； 3）地震微区的不确定性低于地震规范和文献中先前报道的不确定性，表明我们的方法的有效性和精确性。 这项研究的结果显着改进了局部地震响应分析，并强调了深度和空间相关性在理解地震灾害中的关键作用。该数据集可在 https://doi.org/10.5281/zenodo.10885590 上获取（Mori 等人，2024）。