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

断层分段，由几何复杂性定义，如限制弯曲和台阶，可能在阻止地震破裂，从而限制地震的最大规模方面发挥重要作用。在如此复杂的情况下，理解控制断层滑动的机械过程仍然是难以捉摸的。本研究结合野外观测和破裂模拟，评估了走滑地震未能突破中国西北阿尔金断裂双弯曲和步移的200 km长的阿克赛的条件。这个弯曲的两侧，并转移之间的滑动，两个断层链在左阿尔金断裂系统。由于阿克赛弯曲与交叉断层隔离，其行为不太可能受到来自活动断层系统其他部分的应力转移的影响，因此使其成为将模型结果与现场观测进行比较的理想天然实验室。 这项研究将测试基于断层的地震危险性评估，这取决于断层分割，并有助于了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，定义断层分段主要是由专家评估进行的，没有特定于现场的物理基础。数值破裂模拟提供了一个急需的物理基础断层分割，但有显着的局限性。这些局限性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，数值破裂模型对地震危险性绘图的适用性尚未经过测试。结合联合收割机同震破裂和震间断层外应力松弛的多地震周期破裂模型揭示了构造复杂区域的应力状态、地震破裂大小和破裂程度的模式。这个项目将测试这些模式对实地观察，包括古地震，断层滑动速率，断层滑动方向。同时，本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斜三维断层几何形状，通过整合野外观测和数值破裂模拟，本研究跨越学科界限，努力改变对地震破裂过程及其在地质记录中表现形式的理解。在此过程中，该项目建立在国际合作的基础上，具有共同的基础科学研究目标（了解沿着断层的构造过程）和共同的社会需求（了解地震）。这一研究成果将直接影响到对大断层上大地震灾害的认识。例如，获得的见解将直接关系到了解潜在的地震和最南端的圣安德烈亚斯断层破裂的震动危险。

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.