KDI: Large-Scale Inversion-Based Modeling of Complex Earthquake Ground Motion in Sedimentary Basins

该研究项目的主要目标是开发“通过计算机模拟”生成复杂盆地地质和震源的真实基于反演的模型的能力，并利用这种能力在洛杉矶盆地和旧金山湾区地震期间模拟和预测强烈的地面运动。这个问题对减轻地震危害非常重要，因为评估结构在其使用寿命期间的地面运动经验是设计抗震设施和改造现有结构的重要第一步：地面运动建模和预测是设计过程的必要先决条件。该项目涉及卡内基梅隆大学、加州大学伯克利分校和圣地亚哥州立大学的研究人员之间的合作。该研究小组以卡内基梅隆大学为中心，由地震工程师、地震学家、地质学家、计算力学家、计算机科学家以及计算机图形和可视化专家组成。大型盆地地震地面运动的计算机模拟和预测是一项具有挑战性和复杂性的任务，其复杂性来自以下几个方面：盆地响应的多个空间尺度特征（最短波长以几十米为单位，最长波长以公里为单位，盆地尺寸约为几十公里）；时间尺度从解析震源最高频率所需的百分之一秒到盆地内几分钟的震动不等；许多盆地具有高度不规则的几何形状；土壤;材料性能高度不均匀；地质和震源参数只能间接观测到，因此在建模过程中引入了不确定性。目前的地震模拟提供了许多有用的信息，但并不总是能够充分地再现观测到的地震记录。可能的原因是这些模型使用了许多限制性假设来减少计算需求。由于地震地面运动建模需要更高的保真度，研究小组正在开发增强模型，包括以下内容：(1)比当前模型更大数量级的物理域的表示能力；(2)比目前可能的频率更高的建模能力；(3)通过求解三维反演问题，改进现有观测资料的震源模型；(4)基于盆地内地面运动观测反演的盆地物质模型改进；(5)分辨边界面和尖锐界面的能力。地震建模中对更高保真度的追求在模拟过程的所有阶段都引入了计算方面的挑战：从预处理到求解，再到后处理。这是通过在并行三维网格生成、并行三维地震反演和大规模分布式可视化方面的协调一致的努力来解决的。预计这将在物理建模、算法和软件工具开发方面取得重要进展，同时获得对地震地面运动的物理洞察。由于地面运动在基础设施设计中起着至关重要的作用，因此加速使用合适的模拟方法将对公共安全和福利产生直接影响。

The main objective of this research program is to develop the capability to generate realistic inversion-based models of complex basin geology and earthquake sources "by computer simulation" and to use this capability to model and forecast strong ground motions during earthquakes in Los Angeles Basin and the San Francisco Bay Area. This problem is of great importance to earthquake hazard mitigation, since assessing the ground motion experiences by structures during their lifetimes is an essential first step in designing earthquake-resistant facilities, and retrofitting existing structures: ground motion modeling and forecasting are a necessary precursor to the design process. This project involves collaboration between researchers at Carnegie Mellon University, University of California at Berkeley and San Diego State University. The research team, centered at Carnegie Mellon University, consists of earthquake engineers, seismologists, geologists, computational mechanists, computer scientists, and computer graphics and visualization specialist.Computer modeling and forecasting earthquake ground motions in large basins, is a challenging and complex task, with the complexity arising from several sources: multiple spatial scales characterize the basin response (the shortest wavelengths are measured in tens of meters, the longest in kilometers, and basin dimensions are on the order of tens of kilometers); temporal scales vary from the hundredths of a second necessary to resolve the highest frequencies of the earthquake source up to a couple of minutes of shaking within the basin; many basins have highly irregular geometry; the soils; material properties are highly heterogeneous; and geology and source parameters are only indirectly observable, and thus introduce uncertainty into the modeling process. Current earthquake simulations provide much useful information, but are not always capable of adequately reproducing observed seismograms. The likely reason is that these models use a number of restrictive assumptions to reduce the computational requirements. Motivated by the need for greater fidelity in earthquake ground motion modeling the research team is developing enhance models by incorporating the following: (1) The ability to represent physical domains an order of magnitude larger than current models; (2) The ability to model frequencies higher than currently possible; (3) Improved earthquake source models derived from available observation by solving 3D inverse problems; (4) improved basin material models based on the inversion of observations of ground motion within the basin; and (5) The ability to resolve boundary surfaces and sharp interfaces.The drive toward greater fidelity in earthquake modeling introduces computational challenges in all states of the simulation process: from preprocessing, to solving, to postprocessing. This is addressed through a concerted, unified effort in parallel 3D mesh generation, parallel 3D seismic inversion, and large-scale distributed visualization. It is expected that this will result in important advances in physical modeling and algorithm and software tool development for multi-teraflops computers, while gaining physical insight into earthquake ground motion. Because of the critical role that ground motion plays in infrastructure design, the accelerated availability of suitable simulation methodologies will have a direct impact on public safety and welfare.