RAPID/Collaborative Research: Dynamic Site Characterization Following Mw 7.1 Puebla Earthquake for Development of a Refined 3D Shallow Crust Velocity Model of the Mexico City Basin

2017年发生在普埃布拉-墨西哥城的7.1兆瓦地震造成多起建筑物倒塌、地面坍塌和300多人伤亡。记录在案的现场证据揭示了该地区已发表的对以前地震的研究中已认识到的破坏分布模式，特别是复杂的区域和当地地质、水文和岩土条件对塑造墨西哥城粘土沉积物的地面震动特征起着决定性作用。虽然地面运动记录显示了盆地湖区一维(1D)场地放大的明显证据，但据报道在过渡带具有相似沉积深度和结构特征的地区的不均匀破坏分布和地面运动变异性表明，三维(3D)场地效应在所观察到的破坏中发挥了重要作用。墨西哥城场地效应作用的有据可查的证据，结合高密度仪器和数十年的场地特征研究，为工程师和地球科学家提供了一个很好的机会，可以真正研究三维盆地效应和一维局部(浅)场地反应的耦合，以及水文条件和地震放大之间的相互作用。我们对这些现象的理解的进步可以用来为地震活跃地区开发更好的预测模型，包括洛杉矶、旧金山和西雅图等美国大都市地区。这一快速反应研究基金(RAPID)项目的总体目标是将仪器和监测、数据收集和分析以及数值模拟结合起来，以更好地描述地震期间区域盆地和当地场地的影响。快速反应框架将其目标与墨西哥研究人员和工程师正在进行的和即将开展的活动保持一致，以完善盆地的地质和岩土现场特征，并根据该地区迅速变化的水文条件绘制动态岩土特性随时间的演变图，从而最大限度地利用项目资源。该奖项旨在履行国家科学基金会的使命，促进科学进步，促进国民健康、繁荣和福利。在技术层面上，该项目的重点是利用有源源和环境波场面波方法以及水平与垂直频谱比，对墨西哥城的强震站和其他关键地点进行动态场地表征。进行这些测量的目的是开发地震横波速度剖面和估计场地周期，从而为城市和区域危险评估改进微区划图。将现场测量与墨西哥研究数据库中浅层沉积物的空间变异性和深部沉积物的地质信息相结合，将开发出墨西哥城浅层地壳三维速度模型。考虑到软材料中的小尺度横向非均质性对地面运动的影响，特别是在深部地质构造、浅层沉积物和建筑物结构振动特性之间复杂的共振相互作用的情况下，该模型对于基于物理的地面运动模拟是必不可少的。对这些现象的更好理解不仅有助于改进墨西哥城的地震危险性估计，也有助于改善位于类似沉积盆地的美国城市的地震危险性估计。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The 2017 Mw 7.1 Puebla-Mexico City Earthquake caused numerous building collapses, ground failures, and over 300 casualties. Documented field evidence revealed damage distribution patterns that have been recognized in published studies of previous earthquakes in the region, specifically that the complex regional and local geology, hydrology and geotechnical conditions play a decisive role in shaping the ground shaking characteristics of the clay sediments in Mexico City. While ground motion recordings showed clear evidence of one-dimensional (1D) site amplification in the lake zone of the basin, the uneven damage distribution and ground motion variability in areas of reportedly similar deposit depths and structural characteristics in the transition zone suggest that three-dimensional (3D) site effects played a significant role in the observed damage. The documented evidence of the role of site effects in Mexico City combined with the high density instrumentation and decades of site characterization research provide an excellent opportunity for engineers and earth scientists to study in real scale the coupling of 3D basin effects and 1D local (shallow) site response, and the interaction between hydrological conditions and seismic amplification. Advances in our understanding of these phenomena can be used to develop better prediction models for seismically active regions, including U.S. metropolitan areas such as Los Angeles, San Francisco and Seattle. The overarching goal of this Grant for Rapid Response Research (RAPID) project is to combine instrumentation and monitoring, ata collection and analysis, and numerical modeling to better characterize regional basin and local site effects during earthquakes. The rapid response framework maximizes the project resources by aligning its goal with ongoing and upcoming activities of Mexican researchers and engineers to refine the geological and geotechnical site characterization of the basin, and map the evolution of dynamic geotechnical properties with time to the rapidly changing hydrologic conditions in the area. This award addresses the NSF mission to promote the progress of science and to advance the national health, prosperity, and welfare. On a technical level, this project focuses on conducting dynamic site characterization of strong motion stations and other key places in Mexico City using active source and ambient wavefield surface wave methods along with horizontal-to-vertical spectral ratios. The goal of conducting these measurements is to develop seismic shear wave velocity profiles and estimate site periods that can lead to improved microzonation maps for the city and regional hazard assessment. Combining field measurements with the spatial variability of shallow deposits and geological information of the deeper sediments from Mexican research databases, a 3D shallow crust velocity model of Mexico City will be developed. This model is essential for physics based ground motion simulations, given the known influence that small-scale lateral heterogeneities in very soft materials have on ground motions, especially in cases of complex resonance interaction between the deeper geologic formations, the shallow sediments, and the structural vibration characteristics of buildings. A better understanding of these phenomena contributes by extension to improved seismic hazard estimates not only for Mexico City, but also for U.S. cities that lie on similar sedimentary basins.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.