Collaborative Research: Modeling fault ruptures along bends and stepovers

地震发生在断层破裂时，而大地震则是当破裂沿着断层带长距离传播时产生的。大地震经常在数十至数百英里的断层上破裂，包括断层段之间的陡峭(空隙)和断层中的弯曲。这些断层的不规则性也可以阻止破裂的传播。因此，它们对理解地震危险性评估具有重要作用。地震破裂是否能够通过给定的跨度或弯道是非常重要的。此前的研究表明，宽度超过5公里的陡峭地带将阻止破裂的传播，但最近的一些大地震跳过了更大的差距。例如，2016年新西兰7.8级地震涉及断裂跨越断层之间超过15公里宽的缝隙。该项目将使用构造断层模型来模拟初始应力场，特别是在陡坡和弯曲附近，然后利用结果来改进断层破裂模型。该项目的成果将提高我们对大地震及其危害的了解，特别是在断层系统复杂的大陆上。这项研究将在新兴的断层和地震多物理领域培养两名研究生。本科生将参与高级论文研究，研究成果，包括断层破裂的动画，将被纳入德克萨斯农工大学和密苏里大学的本科课程，并免费提供给其他教育工作者。该项目开发的计算机代码将免费与其他研究人员共享。该项目将使用数值模型来模拟断层破裂和沿陡峭和弯曲的传播，断层不规则经常阻止断层破裂，从而限制地震的规模。了解给定的跨度或弯曲是否可以阻止断层破裂的传播对于风险评估至关重要，因为大地震，特别是那些位于陆内走滑断层上的地震，通常通过跳过陡坡并沿着断层弯曲传播来破坏多个断层段。之前的数值模拟和一些野外观测表明，宽度超过5公里的贫瘠将阻止断层破裂；然而，2016年新西兰凯库拉7.8兆瓦地震的破裂在断层之间跳跃了15公里以上。断层几何形状和初始应力是决定破裂行为的最重要因素之一，但在以往的动态破裂模型中，初始应力往往约束较差，被简化为均匀或非均匀的。另一方面，众所周知，应力往往集中在陡峭、弯曲和其他断层不规则部位。该项目将使用断裂构造模型来模拟陡坡和弯曲周围区域静应力的变化，以及由于先前的滑动事件而产生的准静态应力变化。由此产生的应力场将被用于动态破裂模型，以模拟地震期间断层破裂的自发传播。这项研究将使用通用断层模型来探索控制沿陡峭和弯曲破裂的关键参数，然后将开发一个基于2016年凯库拉地震的模型，以深入了解涉及多个断层的复杂破裂。该项目的成果将提高我们对大地震及其危害的了解，特别是在大陆，那里的断层系统复杂，大型事件往往涉及多个断层或分段的破裂。这项研究朝着完全集成的断层力学模型迈出了重要的一步，该模型模拟了多个时间尺度上的应力演变和破裂行为。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Earthquakes occur when faults rupture, and large earthquakes are produced when ruptures propagate long distances along fault zones. Large earthquakes often rupture across tens to hundreds of miles of faults, including stepovers (gaps) between fault segments and bends in faults. These fault irregularities can also stop rupture propagation. So, they play an important role in understanding earthquake hazard assessment. Whether or not an earthquake rupture is able to pass through a given stepover or a bend is very important. Previous studies have suggested that stepovers more than about 5 km wide would stop rupture propagation, but some recent large earthquakes have jumped wider gaps. The 2016 magnitude 7.8 New Zealand earthquake, for example, involved rupture jumping over a gap more than 15 km wide between faults. This project will use tectonic fault models to simulate the initial stress field, especially around stepovers and bends, and then use the results to improve fault rupture models. Results of this project will improve our understanding of large earthquakes and their hazards, particularly within continents where fault systems are complex. This research will train two graduate students in the emerging field of multiphysics in faulting and earthquakes. Undergraduate students will be involved through senior thesis research, and research results, including animations of fault ruptures, will be incorporated into the undergraduate curriculum at Texas A&M and the University of Missouri, and be freely available to other educators. Computer codes developed in this project will be freely shared with other researchers.This project will use numerical models to simulate fault rupture and propagation along stepovers and bends, the fault irregularities that often stop fault rupture, hence limiting the size of earthquakes. Knowing whether or not a given stepover or bend can stop fault rupture propagation is critical for hazard assessment, because large earthquakes, especially those on intracontinental strike-slip faults, usually rupture multiple fault segments by jumping over stepovers and propagating along fault bends. Previous numerical modeling and some field observations have suggested that stepovers more than ~5 km wide would stop fault rupturing; however, ruptures in the 2016 Mw 7.8 Kaikoura earthquake in New Zealand jumped more than 15 km between faults. Fault geometry and initial stress are among the most important factors dictating rupture behavior, but initial stress is often poorly constrained and simplified as homogeneous or ad hoc heterogeneous in previous dynamic rupture models. On the other hand, it is well known that stress tends to concentrate around stepovers, bends, and other fault irregularities. This project will use fault tectonics models to simulate changes of regional static stress around stepovers and bends, and quasi-static stress changes due to previous slip events. The resulting stress fields will then be used in dynamic rupture models to simulate spontaneous propagation of fault ruptures during earthquakes. The research will use generic fault models to explore key parameters controlling rupture along stepovers and bends, and then a model based on the 2016 Kaikoura earthquake will be developed to gain insights into complex ruptures involving multiple faults. Results of this project will improve our understanding of large earthquakes and their hazards, particularly within continents where fault systems are complex and large events often involve rupture of multiple faults or segments. This research takes an important step toward a fully integrated model of fault mechanics that simulates stress evolution and rupture behaviors over multiple timescales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.