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，地震可能始于沿断层的缓慢运动（或“滑动”），然后突然加速为剧烈的快速滑动，从而产生地面震动。在大地震之前已经看到了缓慢滑动，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使用实验室实验和计算机模型来测量和理解大地震前沿断层发生的慢滑和小地震。在实验室的实验中，一块10英尺高的嵌有断层的岩石板被一台巨大的压力机压缩和剪切，使断层蠕变，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——比如粗糙的部分和光滑的部分，或者凸起和弯曲——在提供即将发生地震的警告信号方面发挥了多大的作用。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，将对它们进行大量的地震前缓慢滑动和南极洲冰川下发生的地震数据的测试。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（实验、建模和数据分析）方面的培训。在地震成核理论中，非均质断层的性质——凸起、弯曲、不同岩性和存在于不同尺度上的非均质加载条件——通常不被考虑，但已被证明对地震的发生方式有强烈的影响。在非均质断层上，相邻的断层块在不同的时间到达断裂，通常导致缓慢滑动锋的传播，这种传播可能只能通过地震耦合的逐渐减少来检测，例如在日本东北9级地震之前观察到的，或者从微地震活动的迁移和合并中检测到。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/不稳定的岩石的相互作用。这些机制可能会改变地震发生方式的模型，并更好地为解释前兆活动提供信息。本项目采用米尺度的室内实验，在特定位置施加非均质断层性质，详细研究慢滑锋对地震成核和触发的影响。此外，还建立了非均质断层慢滑传播的理论和数值模型，将实验室结果扩展到与自然地震更相关的长度尺度和条件。然后，这些模型在南极冰川惠兰斯冰流的一个野外尺度的冰川粘滑循环中进行了测试，在那里，地震瞬态影响100公里尺度的冰川粘滑事件，并表现出与实验室观察到的相似的行为。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.