Collaborative Research: The role of subducting seamounts in fault stability and slip behavior throughout the seismic cycle

合作研究：俯冲海山在整个地震周期中断层稳定性和滑动行为中的作用

• 批准号: 2123254
• 负责人: Camilla Cattania
• 金额: $ 25.35万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2123254&HistoricalAwards=false
• 关键词: Collaborative; Research; role; subducting; seamounts

The largest and most destructive earthquakes occur at subduction zones, where one tectonic plate slides underneath another. Relief on the subducting plate, such as seamounts, is thought to affect the frictional resistance and slip behavior. However, it is unclear whether seamounts promote stable slow slip or cause locking of the fault and subsequent earthquakes. Here, the researchers investigate the relationship between seamounts and earthquakes using state-of-the art numerical simulations. They determine how seamounts affect the evolution of rock properties, as they impinge on the overriding plate over hundreds of thousands of years. They calculate variations in rock porosity, strength, and fluid content, which lead to faulting and fracturing. They then calculate how these rock properties, in turn, control slip propagation and the initiation of earthquakes over decades or hundreds of years. By combining simulation codes with different time scales, the team progressively unveils the long-term and short-term factors responsible for triggering large earthquakes. The project outcomes improve earthquake hazard assessment and mitigation in subduction zones. It promotes support for early-career scientists and training for graduate and undergraduate students, notably from underrepresented groups in Earth Sciences. The project is co-funded by both the Geophysics and the Marine Geology and Geophysics programs.Despite significant advances in seismic and geodetic monitoring, the state of locking of the megathrust and its relationship with earthquake ruptures has not been fully characterized. Spatial variations in interseismic coupling and seismic behavior have been attributed to heterogeneities on the megathrust interface. One ubiquitous source of heterogeneity comes from topographic features on the seafloor. As a seamount subducts, it modifies the state of stress on the subduction interface through elastic deformation. It also drives variations in sediment compaction, disruption and fracturing of the upper plate, drainage state, and introduces spatial variations in lithology. The relative importance and interplay of these processes in controlling earthquake processes is still unclear. Here, the researchers investigate the effect of subducting seamounts on the state of stress, slip stability and seismic behavior of the megathrust. They employ two complementary numerical models: (1) a long-term (hundreds of thousands to 1 million years) hydromechanical model with an elastoplastic rheology; the goal is to capture the effect of seamount subduction on material properties and state variables, including sediment compaction and elastic moduli, stresses, and pore pressure. Outputs of this model are then used to set initial conditions and parameters for (2) a short-term (hundreds to thousands of years) elastic earthquake cycle model; the goal is here to study the resulting fault stability and slip behavior. The project overarching goal is a quantitative understanding of the interrelated processes affecting the seismic behavior and interseismic coupling of seamounts, and the spatial relationship between the two. The rapidly growing field of seafloor geodesy will soon provide unprecedented constraints on slip on the megathrust. This study identifies diagnostic features, such as time-dependent locking patterns, which will help interpreting future observations in terms of seismic hazard.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.

最大和最具破坏性的地震发生在俯冲带，在那里一个构造板块滑到另一个板块的下面。俯冲板块上的起伏，如海山，被认为会影响摩擦阻力和滑动行为。然而，尚不清楚海山是促进稳定的缓慢滑动，还是导致断层锁定和随后的地震。在这里，研究人员使用最先进的数值模拟来研究海山和地震之间的关系。它们决定了海底山如何影响岩石性质的演变，因为它们在数十万年的时间里撞击着覆盖在上面的板块。他们计算岩石孔隙度、强度和流体含量的变化，这些变化会导致断层和压裂。然后，他们计算出这些岩石的特性是如何反过来控制滑动传播和几十年或几百年地震的发生的。通过将模拟代码与不同的时间尺度相结合，该团队逐步揭示了引发大地震的长期和短期因素。项目成果改进了俯冲带的地震危险性评估和减灾工作。它促进对早期职业科学家的支持和对研究生和本科生的培训，特别是来自地球科学领域代表性不足的群体。该项目由地球物理和海洋地质与地球物理项目共同资助。尽管在地震和大地测量监测方面取得了重大进展，但巨型逆冲构造的锁定状态及其与地震破裂的关系尚未得到充分表征。大逆冲界面的非均质性导致了震间耦合和地震行为的空间变化。一个普遍存在的异质性来源来自海底的地形特征。海山俯冲时，通过弹性变形改变俯冲界面的应力状态。它还驱动了沉积物压实、上部板块断裂和破裂、排水状态的变化，并引入了岩性的空间变化。这些过程在控制地震过程中的相对重要性和相互作用尚不清楚。在这里，研究人员研究了俯冲海山对巨型逆冲构造的应力状态、滑动稳定性和地震行为的影响。他们采用了两种互补的数值模型：(1)长期（数十万至100万年）的弹塑性流变流体力学模型；目标是捕捉海山俯冲对材料特性和状态变量的影响，包括沉积物压实和弹性模量、应力和孔隙压力。然后将该模型的输出用于设置(2)短期（数百年至数千年）弹性地震周期模型的初始条件和参数；这里的目标是研究由此产生的断层稳定性和滑动行为。该项目的总体目标是定量了解影响海山地震行为和地震间耦合的相关过程，以及两者之间的空间关系。迅速发展的海底大地测量学领域将很快对巨型逆冲断层的滑动提供前所未有的限制。这项研究确定了诊断特征，如时间相关的锁定模式，这将有助于解释未来地震危险方面的观测结果。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。