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Analysis of Fault Growth and Linkage Using Work Minimization

使用功最小化分析故障增长和连锁

基本信息

批准号：
1219919
负责人：
Michele Cooke
金额：
$ 23.21万
依托单位：
University of Massachusetts Amherst
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2012
资助国家：
美国
起止时间：
2012-09-01 至 2015-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1219919&HistoricalAwards=false
关键词：
Analysis Fault Growth Linkage Using

项目摘要

To predict fault growth it is important to understand crack linkage under shear. If fault growth is governed by maximizing mechanical efficiency, a fault system will accommodate deformation either via slip on existing faults or via the growth of a new fault, depending on which is energetically easiest. Consequently, whether small flaws or cracks will link to form a larger crack depends on whether the energetic gain in efficient connection of cracks exceeds the work required to create the linking crack. Using the principle of work minimization, this research project numerically investigates how faults link and grow with two approaches: 1) parametric investigation of crack coalescence in order to test and calibrate the application of work minimization and 2) simulation of the evolution of the San Jacinto fault in southern California. The first approach uses mechanical models in a suite of parametric and stochastic investigations to evaluate the configuration of new fault growth that would both maximize efficiency of the system and are energetically favored to develop, i.e. the work cost is less than the efficiency gained. The stochastic models will incorporate different distributions of flaws in a sample under a variety of loading conditions to explore the effect of differing degrees of anisotropy. Furthermore, an investigation of the scaling of mechanical efficiency from the lab to regional scales will facilitate the second approach employed in the project. The second approach uses three-dimensional models to investigate the work associated with the evolution of a stepover between the Clark fault and the Coyote Creek fault, which are part of the San Jacinto fault in southern California. Numerical models will simulate several stages in the interpreted fault development at this stepover and assess the evolving mechanical efficiency. The study will (a) provide insight into the mechanical efficiency of fracture growth and coalescence, including the impact of anisotropy and the scale of the models; and (b) analyze the development of the San Jacinto fault through the growth and linkage of two fault segments based on the principle of work minimization.Tectonic plate boundaries in the Earth contain many active faults that slip in devastating earthquakes and contribute to building large mountain ranges. The size of potential earthquakes depends on the length of the fault; the larger the fault, the bigger the potential earthquakes. While the behavior of faults is understood, how they grow is not. Within the laboratory, scientists observed that within rocks, smaller cracks link to form fault surfaces. Since many rocks already have abundant small cracks but not all rocks contain faults, we need to understand the conditions that contribute to crack linkage and eventual fault development. This project examines how cracks link to form faults by applying the principle of work minimization. This principle implies that the Earth is lazy. Within a lazy Earth, cracks will only link up if the energetic cost of linking the cracks is less than the energetic benefit of having the cracks linked up. In the case of geologic faults, the benefit is that linked up cracks may more readily accommodate slip and the cost is the energy need to break the rock at the linkage. The project will develop tools to predict crack linkage that are based on work minimization. Once these tools are developed, they will be applied to the San Jacinto fault in southern California, which has a recent history of linkage of two segments. If the model predictions match the interpreted history of the San Jacinto fault then this tool may be of use for investigating other regions of the world and predicting future fault evolution.

为了预测断层的扩展，了解剪切作用下的裂隙连接是很重要的。如果断层的生长受机械效率最大化的支配，断层系统将通过现有断层上的滑动或通过新断层的生长来适应变形，这取决于哪一种在能量上最容易。因此，小的缺陷或裂纹是否会连接成较大的裂纹取决于裂纹有效连接时的能量增益是否超过了产生连接裂纹所需的功。利用功最小化原理，本研究项目用两种方法数值研究了断层是如何连接和生长的：1)为了检验和校准功最小化的应用，对裂缝合并的参数研究；2)模拟加州南部圣哈辛托断层的演化。第一种方法使用一系列参数和随机调查中的力学模型来评估新的故障增长的配置，即工作成本小于获得的效率，该配置既可以最大化系统的效率，又可以大力促进开发。随机模型将在不同的加载条件下包含不同分布的缺陷，以探索不同程度的各向异性的影响。此外，对机械效率从实验室到区域尺度的比例进行调查将有助于项目中采用的第二种方法。第二种方法使用三维模型来研究克拉克断层和郊狼溪断层之间的跨越演化相关的工作，这两个断层是南加州圣哈辛托断层的一部分。数值模型将模拟解释断层在这一跨越阶段的几个发展阶段，并评估不断演变的机械效率。这项研究将(A)深入了解裂缝生长和结合的力学效率，包括各向异性的影响和模型的规模；以及(B)根据功最小化原理，通过两个断层段的生长和连接来分析圣哈辛托断裂的发育。地球上的构造板块边界包含许多活动断裂，这些断裂在毁灭性地震中滑动，并有助于形成大的山脉。潜在地震的大小取决于断层的长度；断层越大，潜在地震就越大。虽然人们了解断层的行为，但它们是如何生长的还不清楚。在实验室内，科学家们观察到，在岩石内部，较小的裂缝连接在一起，形成断层表面。由于许多岩石已经有丰富的小裂隙，但并不是所有的岩石都含有断层，我们需要了解有助于裂隙连接和最终断层发育的条件。这个项目通过应用功最小化原理来研究裂缝是如何连接在一起形成断层的。这一原理意味着地球是懒惰的。在一个懒惰的地球上，只有当连接裂缝的能量成本低于连接裂缝的能量效益时，裂缝才会连接起来。在地质断层的情况下，好处是相连的裂缝可能更容易容纳滑动，而代价是在连接处打破岩石所需的能量。该项目将开发基于功最小化的预测裂纹链接的工具。一旦这些工具被开发出来，它们将被应用于加利福尼亚州南部的圣哈辛托断层，该断层最近有两个部分相连的历史。如果模型预测与圣哈辛托断层的解释历史相匹配，那么这个工具可能会用于调查世界其他地区和预测未来的断层演化。