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

这项研究计划的主要目标是开发“通过计算机模拟”生成复杂盆地地质和地震源的基于真实反演的模型的能力，并利用这种能力来模拟和预测洛杉矶盆地和旧金山湾区地震期间的强烈地面运动。这一问题对减轻地震灾害非常重要，因为评估建筑物在其使用寿命期间经历的地面运动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导。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。以卡内基梅隆大学为中心的研究小组由地震工程师、地震学家、地质学家、计算机械学家、计算机科学家以及计算机图形和可视化专家组成。大型盆地的地震地面运动的计算机模拟和预测是一项具有挑战性的复杂任务，其复杂性来自几个来源：多个空间尺度表征盆地响应(最短的波长以几十米为单位测量，最长的以公里为单位，而盆地的尺寸约为数十公里)；时间尺度从确定震源最高频率所需的百分之一秒到盆地内几分钟的震动；许多盆地具有高度不规则的几何形状；土壤；材料属性高度不均匀；地质和来源参数只能间接观察，因此给建模过程带来了不确定性。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再现观测到的地震图。可能的原因是，这些模型使用了一些限制性假设来减少计算要求。由于地震地面运动模拟需要更高的保真度，研究小组正在开发增强模型，包括以下内容：(1)表示比当前模型大一个数量级的物理域的能力；(2)模拟频率高于当前可能的频率的能力；(3)通过解决3D反问题从现有观测中获得的改进的震源模型；(4)基于盆地内地面运动观测数据的改进的盆地材料模型；在地震模拟中追求更高逼真度的努力在模拟过程的所有状态下都带来了计算挑战：从前处理到求解，再到后处理。这是通过在并行3D网格生成、并行3D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。预计这将导致在物理建模以及用于多万亿次浮点运算的计算机的算法和软件工具开发方面取得重大进展，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扮演的关键角色，合适的模拟方法的加速可获得性将直接影响公共安全和福利。

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.