Collaborative Research: Seismic cycles and earthquake nucleation on heterogeneous faults: Large-scale laboratory experiments, numerical simulations, and Whillans ice stream

根据公认的理论，地震可能是从沿着断层非常缓慢的运动(或“滑动”)开始的，断层突然加速到剧烈的快速滑动，从而引起地面震动。大地震前曾出现过缓慢滑移现象，但通常与理论预测的情况不同。麦克拉斯基博士和他的团队将使用实验室实验和计算机模型来测量和了解大地震前沿断层发生的缓慢滑动和微小地震。在实验室实验中，用巨型压力机压缩和剪切一块10英尺长的岩石，其中嵌入了一个切割(断层)，使断层蠕动，然后在“实验室”地震中突然滑动。这些实验可以测试现实的、非均匀的断层属性--比如粗糙和光滑的部分，或者凸起和弯曲--如何在提供地震即将到来的警告信号方面发挥作用。将开发计算机模型来理解和解释在实验室地震实验中收集的数据。为了检验这些计算机模型的表现如何，他们将与大量关于地震前缓慢滑动和发生在南极洲冰川下的地震的数据进行测试。作为该项目的一部分，三名研究生和至少两名本科生将接受地震科学方面的培训(实验、建模和数据分析)。不均匀的断层属性--存在于不同尺度上的凸起、弯曲、不同的岩性和不同的载荷条件--通常不被考虑在地震成核理论中，但已被证明强烈影响地震引发的方式。在非均质断层上，相邻的断层块在不同的时间达到破坏，通常导致慢滑移锋的传播，这些慢滑移锋可能只有在地震耦合逐渐减弱时才能被检测到，如东北9级地震之前观察到的那样，或者是由于微震活动的迁移和融合。该项目探索了地震周期后期非均质断层的行为，包括慢滑移锋的传播及其与强/不稳定凹凸体的相互作用。这些机制可能会改变地震启动方式的模式，并更好地解释前兆活动。该项目采用米级实验室实验，在特定位置施加非均匀断层属性，详细研究了慢滑移锋对地震成核和触发的影响。此外，还建立了非均质断层上慢滑移传播的理论和数值模型，以将实验室结果扩展到与天然地震更相关的长度尺度和条件。这些模型随后在南极冰川惠兰冰川进行了现场规模的冰川粘滑循环测试，在那里，无地震瞬变会影响100公里规模的冰川粘滑事件，并表现出与实验室中观察到的类似的行为。这一奖项反映了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。

According to well-established theory, earthquakes may start with very slow movement (or "slip") along a fault, which suddenly accelerates to the violently rapid slip that can generate ground shaking. Slow slip has been seen before large earthquakes, but it is usually different from what the theories predict. Dr. McLaskey and his team will use laboratory experiments and computer models to measure and understand slow slip and tiny earthquakes that happen along faults before a large earthquake. In the laboratory experiments, a ten-foot slab of rock with a cut (fault) embedded in it is compressed and sheared using a giant press, making the fault creep and then slip suddenly in "laboratory" earthquakes. The experiments can test how realistic, non-uniform fault properties—like rough versus slippery sections, or bumps and bends—can play a role in providing warning signs of an impending earthquake. Computer models will be developed to understand and explain data collected during the laboratory earthquake experiments. To check how well these computer models perform, they will be tested against a large collection of data on slow pre-earthquake slip and earthquakes that are ocurring beneath a glacier in Antarctica. As part of this project, three graduate students and at least two undergraduates will receive training in earthquake science (experiments, modeling, and data analysis).Heterogeneous fault properties—bumps, bends, differing lithology, and heterogeneous loading conditions that exist at a variety of scales—are generally not considered in earthquake nucleation theories, but have been shown to strongly influence the way an earthquake initiates. On a heterogeneous fault, neighboring fault patches reach failure at different times, often resulting in the propagation of slow slip fronts that may only be detectable as a gradual decrease in seismic coupling, such as that observed prior to the M 9 Tohoku Earthquake, or from the migration and coalescence of microseismicity. This project explores the behavior of heterogeneous faults late in the earthquake cycle including the propagation of slow slip fronts and their interaction with strong/unstable asperities. These mechanisms may transform models of the way earthquakes initiate and better inform the interpretation of precursory activity. This project employs meter-scale laboratory experiments, where heterogeneous fault properties are imposed at specific locations and the effects on earthquake nucleation and triggering by slow slip fronts are studied in detail. Additionally, theoretical and numerical models for slow slip propagation on heterogeneous faults are developed to extend the laboratory results to length scales and conditions more relevant to natural earthquakes. The models are then tested against a field-scale glacial stick-slip cycle at Whillans Ice Stream, an Antarctic glacier, where aseismic transients affect 100 km-scale glacial stick-slip events and exhibit behavior similar to that observed in the lab.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.