The Role of Fault Strands and Roughness in Fault and Earthquake Mechanics

断层链和粗糙度在断层和地震力学中的作用

• 批准号: 0943939
• 负责人: Bruce Shaw
• 金额: $ 14.4万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0943939&HistoricalAwards=false
• 关键词: Role; Fault; Strands; Roughness; Earthquake

The observation that faults are nonplanar, rough rather than flat surfaces,poses a number of challenges in trying to understand how they move. First, modeling such surfaces is difficult numerically. Second, as slip accumulates on a single rough surface, normal stress builds up and the fault soon locks, unable to overcome friction. A standard approach has been to circumvent this lock-up by the method of ``backslipping'', whereby slip is prescribed, and the resulting heterogeneous loading stresses which would allow such prescribed slip to occur are then applied. Unfortunately, the resulting behaviors appear in many ways much closer to how planar faults behave, and thus some of the intrinsic impacts of the geometry appear to be canceled out by this purposefully constructed heterogeneous loading. This project seeks to develop a new approach to the problem, based on the observation that faults occur not as an individual fault surface, but as a system of fault surfaces in a fault zone. In particular, this work will examine fault strands, modeling faults not as one rough surface, but a set of rough surfaces. In this way, the proposal aims to find dynamically consistent fault zones which are both made of rough faults and when loaded uniformly do not lock up. To achieve this goal, take advantage of its anticipated success, and test its implications, three broad research elements would be carried out.First, testing the hypothesis that a system of rough fault strandscan slip under uniform loading without locking up. Continued development and application of a new numerical approach which does not require faults to align with an underlying mesh will open up new realms of study of potential geometry. Constructing and testing correlated sets of rough faults with this numerical approach would then occur. Demonstrating success would be a significant step in understanding and modeling the mechanics of faults. Second, applying the model fault zone to questions relevant to fault and earthquake mechanics. How is slip partitioned in the system? Are there a minimum number of active strands? Does partitioning change as the static coefficient of friction changes? Examining sequences of dynamic ruptures, questions of importance to earthquake mechanics could be asked. Is the distribution of sizes of events on rough faults more Gutenberg-Richter like than on planar faults? Do individual events tend to propagate down one strand, or jump from strand to strand? How often do ruptures break simultaneously multiple strands along-strike? How is slip along-strike related to fault roughness? Third, comparing the model system with geological and seismological observations. Two new measurements quantifying geological observables would be carried out. One measurement concerns quantifying correlations in bends and curvature between neighboring strands. A second measurement concerns measuring the distribution of lateral surface slip strains in large earthquakes. Preliminary work on this showsinteresting potential relationships of typical values of surface slip strain with previous measurements by others of fault roughness. This measurement could provide fundamental constraints on the physics of earthquakes from direct geological observations.Earthquakes pose a number of challenges to society in terms of hazards to public safety and property. Understanding the origins of earthquake behaviors will help us better understand these hazards. This project aims to tackle one of the fundamental questions in earthquake dynamics, and the dynamics of the fault systems on which earthquakes occur, namely, what is the role of the complicated geometry in the problem. Traditional ways of looking at the problem in terms of individual faults, or collections of faults, have run into problems dealing with how to accommodate accumulating slip on nonflat irregular geometries. The PI will examine the role that an observed property of faults, that they occur as fault strands-- multiple surfaces within faults--plays in allowing for slip to accumulate on the nonplanar structures.

观察到断层是非平面的、粗糙的而不是平坦的表面，这给试图理解断层的运动方式带来了许多挑战。首先，对这样的曲面进行数值模拟是困难的。其次，当滑动在一个粗糙的表面上积累时，正常的应力就会增加，断层很快就会锁定，无法克服摩擦。一种标准的方法是通过“反滑动”方法来规避这种锁定，即规定滑动，然后施加导致这种规定滑动发生的非均匀加载应力。不幸的是，由此产生的行为在许多方面更接近于平面断层的行为，因此，这种故意构造的非均匀载荷似乎抵消了几何形状的一些内在影响。这个项目试图开发一种新的方法来解决这个问题，基于观察，断层不是作为一个单独的断层面发生，而是作为一个断层带的断层面系统。特别地，这项工作将检查断层链，将断层建模为一组粗糙的表面，而不是一个粗糙的表面。这样，该方案的目标是寻找由粗糙断层组成的动态一致的断层带，并且在均匀加载时不锁死。为了实现这一目标，利用其预期的成功，并测试其影响，将进行三个广泛的研究要素。首先，测试粗糙断层链系统在均匀载荷下滑动而不锁定的假设。一种不需要断层与底层网格对齐的新数值方法的持续发展和应用将开辟潜在几何研究的新领域。然后用这种数值方法构造和测试相关的粗断层集。证明成功将是理解和模拟断层机制的重要一步。第二，将模型断裂带应用于断层和地震力学的相关问题。滑块在系统中是如何划分的？是否有最小有效链数？分配是否随着静摩擦系数的变化而变化？检查动态破裂序列，可以提出对地震力学重要的问题。粗糙断层上事件大小的分布是否比平面断层更像古腾堡-里希特？单个事件是沿着一条链传播，还是从一条链跳到另一条链？断裂多股同时断裂的频率有多高？沿走向滑动与断层粗糙度有何关系？第三，将模型系统与地质和地震观测结果进行比较。将进行两项量化地质观测的新测量。一种测量方法是量化相邻链之间弯曲和曲率的相关性。第二种测量方法是测量大地震中侧向地表滑动应变的分布。这方面的初步工作表明，地表滑动应变的典型值与以前其他人对断层粗糙度的测量之间存在有趣的潜在关系。这种测量可以从直接的地质观测中对地震的物理性质提供基本的限制。地震在危害公共安全和财产方面给社会带来了许多挑战。了解地震行为的起源将有助于我们更好地了解这些危害。本项目旨在解决地震动力学中的一个基本问题，以及地震发生的断层系统的动力学，即复杂几何在问题中的作用是什么。从单个断层或断层集合的角度来看问题的传统方法在处理如何适应非平坦不规则几何上的累积滑动时遇到了问题。PI将研究观察到的断层特性的作用，即它们以断层链的形式出现——断层中的多个表面——在允许滑动积聚在非平面结构上的作用。