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.

断层分段由几何复杂性定义，如限制弯曲和陡峭，可能在阻止地震破裂从而限制地震的最大尺寸方面发挥重要作用。在如此复杂的情况下控制断层滑动的机械过程仍然难以理解。本研究结合野外观测和破裂模拟，对走滑地震未能突破中国西北部阿尔金断裂双弯跨断带200公里长的阿克赛断裂的条件进行了评价。该弯曲位于阿尔金-塔格断裂系统左侧的两条断裂带的两侧，并在两条断裂带之间滑动。由于Aksay弯曲与相交的断层隔离，其行为不太可能受到来自活动断层系统其他部分的应力传递的影响，因此使其成为将模型结果与现场观测进行比较的理想自然实验室。这项研究将测试基于断层的地震危险性评估，这种评估依赖于断层分段，并有助于理解永久变形是如何在断层和周围地壳之间划分的。到目前为止，确定故障分段主要是由专家评估执行的，没有特定地点的物理基础。数值破裂模拟为断层分割提供了急需的物理基础，但也有很大的局限性。这些限制包括地震前的应力状态是未知的，在几何复杂的区域不太可能是平滑的。因此，数值破裂模型在地震危险性图中的适用性仍未得到检验。多地震旋回破裂模型结合了同震破裂和震间断层间应力松弛，揭示了构造复杂区的应力状态、地震破裂大小和破裂程度的模式。该项目将根据包括古地震学、断层滑移率和断层滑动方向在内的现场观测来测试这些模式。同时，这项研究将推进这些数值模型的最新发展，包括断层外塑性和倾角，三维断层几何。通过将现场观测和数值破裂模拟相结合，本研究跨越了学科界限，努力改变对地震破裂过程及其在地质记录中的表现的理解。通过这样做，这个项目建立在具有共同的基础科学研究目标(了解沿断层的构造过程)和共同的社会需求(了解地震)的国际合作的基础上。这项研究的结果将直接影响对主要断层上大地震危害的了解。例如，所获得的洞察力将与了解潜在的地震和最南端圣安德烈亚斯断层破裂造成的震动危险直接相关。