Collaborative Research: Controls on Termination of Great Earthquakes in a Restraining Double-Bend of the Altyn Tagh Fault

合作研究：阿尔金断裂带约束性双弯对大地震终止的控制

• 批准号: 1049834
• 负责人: Benchun Duan
• 金额: $ 20.31万
• 依托单位: Texas A&M Research Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-04-01 至 2015-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1049834&HistoricalAwards=false
• 关键词: Collaborative; Research; Controls; Termination; Great

Fault segmentation, defined by geometric complexities such as restraining bends and stepovers, may play an important role in arresting earthquake rupture and thus limiting the maximum size of earthquakes. Understanding the mechanical processes that control fault slip within such complexities remains elusive. This study integrates field observations and rupture modeling to assess the conditions under which strike-slip earthquakes fail to break across the 200 km-long Aksay restraining double bend and stepover of the Altyn Tagh fault in northwestern China. This bend is flanked by, and transfers slip between, two fault strands within the left-lateral Altyn Tagh fault system. Because the Aksay bend is isolated from intersecting faults, its behavior is unlikely to be affected by stress-transfer from other parts of the active fault system, thus making it an ideal natural laboratory to compare model results against field observations. This research will test fault-based seismic hazard assessments that depend upon fault segmentation, and contribute understanding of how permanent deformation is divided among faults and the surrounding crust. To date, defining fault segmentation has been performed largely by expert assessment, with no site-specific physical basis. Numerical rupture simulations offer a much-needed physical foundation for fault segmentation, but with significant limitations. These limitations include that the pre-earthquake stress-state is unknown and unlikely to be smooth in zones of geometric complexity. Thus, the applicability of numerical rupture models to seismic hazard mapping remains untested. Multi-earthquake cycle rupture models that combine coseismic rupture with interseismic off-fault stress relaxation reveal patterns of stress-states, earthquake rupture sizes, and rupture extents in zones of structural complexity. This project will test these patterns against field observations including paleoseismology, fault slip-rates, and fault-slip direction. Simultaneously, this research will advance the state-of-the-art of these numerical models to include off-fault plasticity, and dipping, three-dimensional fault geometries.By integrating field observations and numerical rupture modeling, this research cuts across disciplinary boundaries in an effort to transform understanding of the earthquake rupture process and its manifestation in the geologic record. In so doing, this project builds upon an international collaboration with shared basic-science research objectives (to understand tectonic processes along faults) and shared societal need (to understand earthquakes). The outcomes of this research will directly affect understanding of hazards from great earthquakes on major faults. For example, the insights gained will be of direct relevance to understanding potential earthquakes and shaking hazards from rupture of the southernmost San Andreas fault.

故障分段是由几何复杂性（例如限制弯曲和踏板）定义的，可能在阻止地震破裂并因此限制地震的最大大小中起重要作用。了解控制故障滑移在此类复杂性内的机械过程仍然难以捉摸。这项研究集成了现场观察和破裂建模，以评估在中国西北部的阿尔蒂·塔格（Altyn Tagh）断层的200 km长达200公里的Aksay限制双弯道和阶梯范围内破裂的条件。该弯曲是在左侧Altyn Tagh故障系统内的两条断层链之间的两侧，并在之间滑动。由于Aksay弯曲是从相交断层中分离出来的，因此其行为不太可能受到活性断层系统其他部分的压力转移的影响，因此使其成为将模型结果与现场观察结果进行比较的理想天然实验室。 这项研究将测试依赖断层分段的基于断层的地震危险评估，并有助于理解断层和周围地壳之间的永久变形。迄今为止，定义故障细分主要是通过专家评估进行的，没有特定地点的物理基础。数值破裂模拟为故障分割提供了急需的物理基础，但具有重大限制。这些局限性包括锻炼前应力状态是未知的，在几何复杂性区域中不太可能平滑。因此，数值破裂模型在地震危险映射中的适用性仍未测试。将coseis震破裂与跨型over损应力放松相结合的多锻炼周期破裂模型揭示了压力态，地震破裂大小和结构复杂性区域中的破裂量的模式。该项目将测试这些模式，以针对野外观察结果进行测试，包括古介质学，断层滑动率和断层滑移方向。同时，这项研究将使这些数值模型的最先进，包括越野可塑性和浸入，三维故障几何形状。通过整合现场观测和数值破裂建模，这项研究逐渐跨越了纪律界限，以努力改变地震破裂过程的理解及其在地球上表现出的地球形式的理解。这样一来，这个项目就建立在国际合作与共同基本科学研究目标（以了解沿故障沿线的构造过程）和共同的社会需求（了解地震）的国际合作。这项研究的结果将直接影响对主要断层大地震的危害的理解。例如，获得的见解将与理解潜在的地震和避开最南端的圣安德烈亚斯断层破裂的危害直接相关。