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，地震可能从沿着断层的非常缓慢的运动（或“滑动”）开始，然后突然加速到可以产生地面震动的剧烈快速滑动。在大地震之前已经看到了缓慢的滑动，但它通常与理论预测的不同。麦克拉斯基博士和他的团队将利用实验室实验和计算机模型来测量和理解大地震前沿着断层发生的慢滑和小地震。 在实验室的实验中，一块10英尺长的岩石板上嵌入了一个切口（断层），用一台巨大的压力机压缩和剪切，使断层蠕动，然后在“实验室”地震中突然滑动。这些实验可以测试真实的、不均匀的断层特性，比如粗糙与光滑的断层，或者颠簸和弯曲，在提供即将发生的地震的预警信号方面可以发挥多大的作用。将开发计算机模型来理解和解释实验室地震实验期间收集的数据。为了检查这些计算机模型的性能，他们将对大量关于地震前缓慢滑动和南极冰川下发生的地震的数据进行测试。作为这个项目的一部分，三名研究生和至少两名本科生将接受地震科学（实验、建模和数据分析）方面的培训。非均匀断层性质--隆起、弯曲、不同岩性和存在于各种尺度的非均匀载荷条件--通常不在地震成核理论中考虑，但已被证明强烈影响地震的发生方式。在非均匀断层上，相邻的断层块在不同的时间达到破坏，通常导致缓慢滑动前锋的传播，这可能只能通过地震耦合的逐渐减少来检测，例如在M9东北地震之前观察到的，或者来自微震活动的迁移和合并。该项目探讨了地震周期后期非均质断层的行为，包括慢滑锋的传播及其与强/不稳定凸体的相互作用。这些机制可能会改变地震发生方式的模型，并更好地为地震活动的解释提供信息。该项目采用米级实验室实验，在特定位置施加非均质断层特性，并详细研究了慢滑锋对地震成核和触发的影响。此外，理论和数值模型慢滑动传播的非均质断层扩展的实验室结果的长度尺度和条件更相关的天然地震。然后，该模型进行测试，对一个领域规模的冰川粘滑循环在Whillans冰流，南极冰川，在南极洲的冰川瞬变影响100公里规模的冰川粘滑事件，并表现出类似的行为在实验室中观察到的。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

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.