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

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构造板块之下。俯冲板块上的地形，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促进了稳定的缓慢滑动，还是导致了断层的锁定和随后的地震。在这里，研究人员使用最先进的数值模拟研究海山和地震之间的关系。它们决定了海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了覆盖的板块。 他们计算岩石孔隙度、强度和流体含量的变化，这些变化导致断层和断裂。然后，他们计算这些岩石特性如何反过来控制几十年或几百年的滑动传播和地震的发生。 通过结合不同时间尺度的模拟代码，该团队逐步揭示了引发大地震的长期和短期因素。项目成果改善了俯冲带的地震灾害评估和减灾工作。 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中代表性不足的群体。 该项目由地球物理方案和海洋地质与地球物理方案共同供资，尽管在地震和大地测量监测方面取得了重大进展，但尚未充分确定巨型逆冲断层的锁定状态及其与地震破裂的关系。地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的不均匀性。海底地形特征是造成不均匀性的一个普遍原因。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。它还驱动了沉积物压实、上板块破裂和断裂、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仍然不清楚。在这里，研究人员调查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。它们采用了两个互补的数值模型：（1）一个长期（数十万年至100万年）的流体力学模型，具有弹塑性流变学;目标是捕捉海山俯冲对物质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，该模型的输出被用于设置（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从数量上了解影响海山地震行为和震间耦合的相互关联的过程，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功能，如随时间变化的锁定模式，这将有助于解释未来的观测地震hazards.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.