NEESR-SG: High-fidelity site characterization by experimentation, field observation, and inversion-based modeling

摘要0619078该奖项是美国国家科学基金会06-504计划征集“小乔治·E·布朗地震工程模拟研究网络”竞赛的结果。该项目团队包括卡内基梅隆大学、佐治亚理工学院、加州大学圣巴巴拉分校、德克萨斯大学埃尔帕索分校和德克萨斯大学奥斯汀分校。这项研究的主要目标是发展评估单个场地和整个盆地的地质结构和力学性质的能力，并在加纳山谷井下阵列(GVDA)的Nees@UCSB场地和整个加纳山谷展示这一能力。具体地说，这一高保真估计将基于：(A)利用德克萨斯大学奥斯汀分校(Nees@UTexas)的NEES设备进行的现场动态激发；(B)来自新的强震和宽带传感器网络的地震记录；以及(C)基于偏微分方程(PDE)约束优化的新的反演方法。这个项目代表着一个无与伦比的机会，将最先进的现场实验与最先进的计算工具结合起来，以达到以分辨率和长度尺度成像地下表面的目的，直到最近还无法实现。选择这两个NEES站点的原因如下：(1)Nees@UTexas站点的移动振动器可以在广泛的频率和负载水平上施加负载。结合地震记录，收集的数据将允许估计主波和横波的速度。此外，土壤阻尼将包括在反演模型中，将与两个速度同时估计；以及(2)GVDA(Nees@UCSB)是一个试验场，位于加利福尼亚州南部高地震区的一个狭窄山谷中，非常适合监测地面运动。在过去15年里，在该地点和整个山谷的其他自由表面位置记录到的数百次小地震，使其成为区域深部结构反演和通过野外试验独立核实场地反演的宝贵数据来源。为了提高倒置模型的保真度，该数据集将使用来自EarthScope的USArray组件的仪器的数据进行扩充，这些数据将在与活动测试期间重叠的一段时间内部署。现场测试将为确定GVDA现场和整个山谷上层的特征提供数据。这些试验的观测，包括井下和自由地面，将与地震观测一起用于获得二维和三维高保真剖面。此外，这些观测将与表面波谱分析(SASW)方法一起使用，以获得测试地点的横波速度剖面。该速度分布将被用作基于全局优化的逆局部和区域模型的盲测验证套件的一部分。虽然综合方法将适用于南加州的一个特定地区，但其结果将适用于美国和国外的许多其他地区。新的综合方法将同样适用于利用波进行探测的类似问题，例如石油和天然气勘探界出现的问题、医学成像应用、其他基础设施条件评估问题，如结构缺陷识别问题、评估候选核废料场地的适宜性，甚至是场地特征至关重要的遥控行星探测飞行任务。由于土壤在基础设施设计中起着至关重要的作用，可靠的土壤表征方法的加速可获得性将直接影响公共安全和福利。

Abstract 0619078 This award is an outcome of the NSF 06-504 program solicitation "George E. Brown, Jr. Network for Earthquake Engineering Simulation Research (NEESR)" competition. The project team includes Carnegie Mellon University; Georgia Institute of Technology; the University of California at Santa Barbara; the University of Texas, El Paso; and The University of Texas at Austin. The main objective of this research is to develop the capability for estimating the geological structure and mechanical properties both of individual sites and of complete basins, and to demonstrate this capability on the nees@UCSB site at the Garner Valley Downhole Array (GVDA) and the entire Garner Valley. Specifically, this high-fidelity estimation will be based on integrating: (a) in-situ dynamic excitation using the NEES equipment at the University of Texas at Austin (nees@UTexas); (b) earthquake records from new strong-motion and broadband sensor networks; and (c) new inversion methods based on partial-differential-equation (PDE)-constrained optimization. This project represents an unparalleled opportunity to couple state-of-the-art field experimentation with state-of-the-art computational tools for the purpose of imaging the subsurface at resolutions and length scales until recently unattainable. These two NEES sites were selected for the following reasons: (1) The mobile shakers at the nees@UTexas site can apply loads at a wide range of frequencies and loading levels. Coupled with earthquake records, the data collected will permit the estimation of the primary- and shear-wave velocities. In addition, soil damping will be included in the inversion models, to be estimated simultaneously with the two velocities; and (2) The GVDA (nees@UCSB) is a test site located in a narrow valley in a highly seismic region in southern California, which is ideally suited for monitoring ground motion. The hundreds of small earthquakes that have been recorded at the site and at other free surface locations throughout this valley in the last 15 years make it an invaluable source of data for the regional deep structure inversions, and for an independent verification of site inversion through field tests. To increase the fidelity of the inverted models, this dataset will be augmented with data from instruments of the USArray component of EarthScope that will be deployed over periods of time that will overlap the periods of active testing. In-situ tests will provide data for characterizing the upper layers at the GVDA site and throughout the valley. Observations from these tests, both downhole and on the free surface, will be used, along with earthquake observations, for obtaining two-dimensional and three-dimensional, high-fidelity profiles. In addition, these observations will be used with the spectral-analysis-of-surface-waves (SASW) method to obtain the shear-wave velocity profile at the test locations. This velocity profile will be used as part of the blind-test validation suite of the global optimization-based inverse local and regional models. While the integrated methodology will be applied to a specific region in southern California, the results will be applicable to many other regions in the United States and abroad. The new integrated methodology will be equally applicable to similar problems where waves are used for probing, such as those arising in the oil and gas exploration communities, medical imaging applications, other infrastructure condition-assessment problems such as in structural flaw identification problems, assessing the suitability of candidate nuclear waste sites, and even remotely-controlled planetary exploration missions where site characterization is of paramount importance. Because of the critical role that soils play in infrastructure design, the accelerated availability of reliable soil characterization methods will have a direct impact on public safety and welfare.