Collaborative Proposal: Testing Collision Versus Frictional Stress-Drop Models of High-Frequency Earthquake Ground Motions

地震是无处不在的自然灾害，影响着全球活跃断层系统附近的弱势群体。尽管科学界进行了长期而深入的研究，但对地震破裂过程的几个关键方面仍然知之甚少。这个项目的重点是了解地震断层相互滑动时破裂过程中产生的高频地震能量的物理来源。科学认识方面的这些进展对减轻地震危害具有广泛的影响，为未来应如何制定建筑设计规范提供了信息，以防止地震对脆弱结构造成破坏。该项目还支持早期职业科学家，并为传统上在地球科学领域代表性不足的群体提供研究机会。通过有针对性的推广工作，该项目将吸引来自不同社会经济背景的高中生，旨在通过体验式学习指导他们未来的职业生涯。传统上，高频地面运动的物理起源是用摩擦模型来解释的，该模型假设断层滑动期间的摩擦过程决定了应力降等破裂特性，从而控制了震动幅度。然而，这些经典的摩擦模型往往难以解释在自然界中观察到的高频地面运动的许多方面。这种差异导致了一种假设，即为适应断层系统的几何复杂性而发生的断裂带结构的弹性冲击可能在高频地面运动的产生中起重要作用。该项目将使用三组地震学观测来明确验证这一假设——拐角频率、辐射模式和s波与p波辐射能量的比率——摩擦模型和撞击模型对此做出了截然不同的预测。这项工作对我们理解地震破裂的物理学有许多重要的意义，包括确定需要对断裂带结构进行详细测量以进行准确的地面运动预测的程度，修改地震应力降估计的物理解释，以及限制地壳中波散射的程度。从整体上看，这些进展将为未来的地震减灾工作提供关键的观测限制。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。

Earthquakes are ubiquitous natural hazards that impact vulnerable populations near active fault systems across the globe. Despite longstanding and intensive research by the scientific community, several key aspects of the earthquake rupture process remain poorly understood. This project focuses on understanding the physical origin of the high-frequency seismic energy that is generated during the rupture process as earthquake faults slip past one another. These advances in scientific understanding have broad implications for earthquake hazard mitigation, informing how future building design codes should be constructed in order to prevent earthquake damage to vulnerable structures. The project also supports early career scientists and provides research opportunities to traditionally underrepresented groups in the geosciences. Through targeted outreach efforts, the project will engage high school students from a diverse range of socioeconomic backgrounds, with an aim toward experiential learning that will guide them in their future careers.The physical origins for high-frequency ground motions have traditionally been explained in terms of a frictional model that postulates that frictional processes during fault slip determine rupture properties like stress drop, which in turn control shaking amplitudes. However, these classical frictional models often struggle to explain many aspects of the high-frequency ground motions observed in nature. This discrepancy has led to the hypothesis that elastic impacts of fault-zone structures that occur to accommodate the geometric complexity of fault systems may play an important role in the generation of high-frequency ground motions. The project will explicitly test this hypothesis using three sets of seismological observations – corner frequencies, radiation patterns, and the ratio of S-wave to P-wave radiated energy – for which the frictional and impact models make distinctly different predictions. This work has a number of important implications for our understanding of the physics of earthquake rupture, including determining the degree to which detailed measurements of fault zone structure are needed to make accurate ground motion predictions, revising the physical interpretation of seismological stress drop estimates, and constraining the degree of wave scattering in the Earth’s crust. These advances, taken holistically, will provide crucial observational constraints for future earthquake hazard mitigation efforts.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.