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: 2123255
• 负责人: Demian Saffer
• 金额: $ 16.79万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing 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=2123255&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、最具破坏性的地震发生在俯冲带，即一个板块滑向另一个板块下方的区域。俯冲板块上的地形（例如海山）被认为会影响摩擦阻力和滑动行为。 然而，目前尚不清楚海山是否促进稳定的慢滑移或导致断层锁定和随后的地震。在这里，研究人员利用最先进的数值模拟研究了海山和地震之间的关系。它们决定了海山在数十万年的时间里撞击最上面的板块时如何影响岩石特性的演变。 他们计算导致断层和破裂的岩石孔隙度、强度和流体含量的变化。然后，他们计算出这些岩石特性如何在数十年或数百年内控制滑移传播和地震的发生。 通过结合不同时间尺度的模拟代码，团队逐步揭示了引发大地震的长期和短期因素。该项目成果改善了俯冲带的地震灾害评估和缓解措施。 它促进对早期职业科学家的支持以及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的学生。 该项目由地球物理学和海洋地质和地球物理学项目共同资助。尽管地震和大地测量监测取得了重大进展，但巨型逆冲断层的锁定状态及其与地震破裂的关系尚未得到充分表征。震间耦合和地震行为的空间变化归因于巨型逆冲断层界面上的非均质性。异质性的普遍来源之一来自海底的地形特征。当海山俯冲时，它通过弹性变形改变俯冲界面上的应力状态。它还驱动沉积物压实、上部板块的破坏和破裂、排水状态的变化，并引入岩性的空间变化。这些过程在控制地震过程中的相对重要性和相互作用仍不清楚。在这里，研究人员研究了俯冲海山对巨型逆冲断层的应力状态、滑动稳定性和地震行为的影响。他们采用两个互补的数值模型：（1）具有弹塑性流变学的长期（数十万至一百万年）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，该模型的输出用于设置（2）短期（数百至数千年）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震间耦合的相互关联过程以及两者之间的空间关系。快速发展的海底大地测量领域很快将为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，例如时间相关的锁定模式，这将有助于解释未来在地震危险方面的观测结果。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查进行评估，被认为值得支持标准。