Robust site characterization and ground response analysis require a thorough understanding of subsurface features, including geophysical properties and geometries of sediment bodies. Late Quaternary paleovalley systems, often overlooked in seismic hazard assessments, represent a potential threat due to their unconsolidated infill (with shear wave velocities <200 m/s) and sharp contrast with the adjacent substrate. Through an integrated approach that combined geophysical and stratigraphic data, we characterized the subsurface of the Pescara paleovalley system. Geostatistical interpolation of microtremor measurements enabled mapping resonance frequencies, highlighting abrupt changes and delineating the paleovalley boundaries. High-resolution core descriptions were then correlated with resonance frequencies, enabling the reconstruction of a 3D geophysical depth model of the buried paleovalley morphology. Furthermore, analyzing velocity profiles from down-hole tests led to the identification of five main seismic/stratigraphic layers within the valley fill. The geometry and facies architecture were reconstructed through a cross-section transversal to the paleovalley axis and then implemented into a 2D finite element model. Seismic response was computed, revealing significant amplification factors at frequencies closely matching the direct observations. Amplification factors peaked at frequencies between 0.9 and 1.1 Hz in the paleovalley center and up to 5.5 Hz towards the flanks, reaching a factor of 4.6. These findings suggest a notable increase in amplification amplitude compared to simpler geological contexts and emphasize the potential impact on common building types. Response spectra show strong amplifications in the paleovalley system, potentially leading to an underestimation of spectral accelerations compared to NTC18 guidelines. The comparisons of 1D and 2D modeling approaches revealed minimal differences, indicating that the generally flat geometry of the valley may not exhibit clear 2D effects. However, local subsurface stratigraphy strongly influences lateral changes in seismic response, emphasizing the importance of detailed subsurface knowledge for realistic seismic response estimates.

中文翻译：

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晚第四纪古河谷系统的地震放大：佩斯卡拉古河谷（意大利中部）的二维地震响应分析


稳健的场地表征和地面响应分析需要彻底了解地下特征，包括沉积物的地球物理特性和几何形状。晚第四纪古河谷系统在地震灾害评估中经常被忽视，但由于其松散的填充物（剪切波速度为 <200 m/s）以及与邻近基底的鲜明对比，因此构成了潜在的威胁。通过结合地球物理和地层数据的综合方法，我们描述了佩斯卡拉古山谷系统的地下特征。微震测量的地统计插值能够绘制共振频率图，突出突兀的变化并描绘古山谷边界。然后将高分辨率岩心描述与共振频率相关联，从而能够重建埋藏古谷形态的 3D 地球物理深度模型。此外，通过分析井下测试的速度剖面，确定了山谷填充物内的五个主要地震/地层。通过横向于古谷轴的横截面重建几何形状和相结构，然后将其应用到二维有限元模型中。计算了地震响应，揭示了与直接观测结果密切匹配的频率下的显着放大系数。古谷中心的放大系数在 0.9 至 1.1 Hz 之间的频率处达到峰值，向侧翼的放大系数达到 5.5 Hz，达到 4.6 倍。这些发现表明，与更简单的地质环境相比，放大幅度显着增加，并强调了对常见建筑类型的潜在影响。 响应光谱显示古谷系统中存在强烈的放大，与 NTC18 指南相比，可能导致光谱加速度的低估。一维和二维建模方法的比较显示出最小的差异，表明山谷的基本平坦的几何形状可能不会表现出明显的二维效果。然而，当地地下地层学强烈影响地震响应的横向变化，强调了详细的地下知识对于实际地震响应估计的重要性。