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年普埃布拉-墨西哥城7.1级地震造成大量建筑物倒塌，地面故障和300多人伤亡。 记录在案的现场证据显示，已在该地区以前的地震，特别是复杂的区域和当地的地质，水文和岩土工程条件发挥了决定性的作用，塑造在墨西哥城的粘土沉积物的地面震动特性的已发表的研究中认识到的损害分布模式。 虽然地面运动记录显示了明确的证据，一维（1D）网站放大在湖泊区的盆地，不均匀的损害分布和地面运动的变化，据报道，类似的存款深度和结构特征的过渡区表明，三维（3D）网站的影响发挥了重要作用，在所观察到的损害。 墨西哥城场地效应作用的证据记录，结合高密度仪器和数十年的场地特性研究，为工程师和地球科学家提供了一个极好的机会，以研究真实的尺度的三维盆地效应和一维局部（浅层）场地响应的耦合，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，弗朗西斯科和西雅图等美国大都市地区。 快速反应研究（RAPID）项目的总体目标是将联合收割机仪器和监测、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。 快速反应框架通过将其目标与墨西哥研究人员和工程师正在进行和即将进行的活动相结合，最大限度地利用项目资源，以完善盆地的地质和岩土工程场地特征，并根据该地区迅速变化的水文条件绘制动态岩土工程特性随时间的演变图。 该奖项致力于NSF的使命，以促进科学的进步和促进国家的健康，繁荣和福利。在技术层面上，该项目的重点是利用有源和环境波场表面波方法沿着水平与垂直频谱比，对墨西哥城的强震台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绘制地震剪切波速度剖面图，并估计场地周期，从而改进城市和区域灾害评估的小区划图。 将实地测量结果与墨西哥研究数据库中浅层沉积物的空间变异性和深层沉积物的地质信息相结合，建立墨西哥城三维浅层地壳速度模型。 该模型是必不可少的基于物理的地面运动模拟，鉴于已知的影响，小规模的横向不均匀性在非常软的材料对地面运动，特别是在复杂的共振相互作用的情况下，更深的地质构造，浅层沉积物，和建筑物的结构振动特性。 对这些现象的更好理解不仅有助于墨西哥城的地震危险性评估，也有助于位于类似沉积盆地上的美国城市的地震危险性评估。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.