Abstract The Sun Pyramid in Teotihuacan, Mexico, belongs to the cultural heritage of Mexico and the world. Built nearly a millennium ago, the Pyramid is poorly known in terms of its mechanical properties. In order to assess these properties, we measured and studied the ambient seismic noise which is becoming a tool to explore non-invasively geological structures. This research is aimed to contribute to the structural diagnosis and seismic vulnerability assessment of this emblematic Mexican pre-Hispanic monument. We analyzed the horizontal-to-vertical spectral ratio and the cross-correlations of seismic ambient noise recorded during four hours by 15 broadband stations, distributed on different levels of the structure, and propose a three-dimensional velocity model for the Sun Pyramid in Teotihuacan. The processed data includes the stacking of cross-correlations. We identified arrivals corresponding to a rich mixture of body and surface waves. Group velocity dispersion curves were extracted from the symmetrized cross-correlation of vertical displacements between station pairs. The retrieved travel times between station pairs allowed a tomographic analysis based on the Fast Marching Method (FMM). Besides, simultaneous inversions of the local dispersion curves (obtained from the group velocity tomography) and the HVSR mitigate non-uniqueness of the retrieved Vp and Vs. Our wave-velocity model reveals two main features of the Sun Pyramid: i) The low-velocity anomalies in the cover layer correlate well with the presence of support walls or counterforts that, apparently, were part of the construction technique seeking to provide support to weak parts of the Sun Pyramid. ii) The core of the structure, with soft material subjected to the action of infiltrated water, is susceptible to causing wall failures. These results could be useful to design conservation strategies for this emblematic Mexican pre-Hispanic monument.

中文翻译：

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通过被动地震方法对太阳金字塔（墨西哥特奥蒂瓦坎）的结构进行成像

摘要 墨西哥特奥蒂瓦坎的太阳金字塔是墨西哥乃至世界的文化遗产。金字塔建于近千年前，其机械性能鲜为人知。为了评估这些特性，我们测量并研究了环境地震噪声，该噪声正成为探索非侵入性地质结构的工具。这项研究旨在为这座具有象征意义的墨西哥前西班牙裔纪念碑的结构诊断和地震脆弱性评估做出贡献。我们分析了分布在结构不同层次的 15 个宽带台站在 4 小时内记录的地震环境噪声的水平垂直谱比和互相关，并提出了特奥蒂瓦坎太阳金字塔的三维速度模型. 处理后的数据包括互相关的叠加。我们确定了与体波和表面波的丰富混合相对应的到达。从站对之间垂直位移的对称互相关中提取群速度频散曲线。检索到的站点对之间的旅行时间允许基于快速行进方法 (FMM) 进行断层扫描分析。此外，局部色散曲线（从群速度断层扫描获得）和 HVSR 的同时反演减轻了检索到的 Vp 和 Vs 的非唯一性。我们的波速模型揭示了太阳金字塔的两个主要特征：i) 覆盖层中的低速异常与支撑墙或堡垒的存在密切相关，显然，是寻求为太阳金字塔薄弱部分提供支撑的建筑技术的一部分。ii) 结构的核心，软材料受到渗透水的作用，容易导致墙体失效。这些结果可能有助于为这座具有象征意义的墨西哥前西班牙裔纪念碑设计保护策略。