Collaborative Research: Variation of Incoming Plate Hydration and Faulting Along the Alaska Subduction Zone

俯冲带是固体地球、水圈和大气之间进行重要化学交换的场所。渗入俯冲洋板块的海水与含水矿物结合，并被带到地球深处。 随着俯冲板块下降和升温，水被释放出来，并可能影响俯冲带断层的性质，俯冲带地震的产生，以及供给弧火山的岩浆的产生。一些水通过火山爆发被释放回大气中。 在这个循环中，一个关键的未知数是即将到来的构造板块中水的数量和分布。 盘子里储存了多少水？水能渗透到盘子的多深？板块中的水量是否沿着俯冲带而变化？如果是这样，是什么控制了这种变化？ 该项目将利用在科迪亚克岛和舒马金群岛之间的阿拉斯加俯冲带收集的地震和测深（海底深度）数据，以限制俯冲大洋板块中储存的水量和分布。这些结果对于了解阿拉斯加俯冲带这一部分大地震发生的变化和岩浆供给火山的成分将是有价值的。 研究生和本科生将参与数据分析并获得有价值的培训。水的体积和分布被认为控制着俯冲带的许多基本过程，包括巨型逆冲行为，弧岩浆的生成和中等深度的地震。然而，由于大洋板块的到来，进入俯冲带的水量仍然存在争议，人们对此知之甚少，导致地球深水预算存在很大的不确定性。 此外，沿走向变化的水输入，其影响沿走向变化的俯冲过程中，也约束不足。 从阿拉斯加两栖动物社区地震实验（AACSE）新获得的地震和测深数据将与阿拉斯加半岛以外的现有数据相结合，以确定整个传入海洋岩石圈的外部隆起断层和可能的水合作用。这个俯冲带是一个很好的研究目标，因为它表现出沿走向的变化，在一系列深度的巨型逆冲断层耦合和地震活动，现有的数据表明，沿走向的断层和水化的变化。将使用地震面波、体波和活动震源方法确定传入地壳和地幔中含水相的横向和深度分布，并将结果与传入板块地震活动和测深绘制的断层进行比较。地震各向异性将对断裂带周围水化矿物的分布提供限制。结果将提供一个全面的估计的传入板水预算作为一个功能的位置沿着阿拉斯加俯冲带，允许水对其他俯冲过程的影响进行定量评估。 新的限制传入的水预算可用于多学科研究，评估水的影响，大推力和中间深度的地震活动特征，沿走向火山输出的变化，并对全球地幔水预算。对传入板块正断层的最大尺寸的估计将允许对此类地震可能的海啸危险进行评估。该奖项反映了NSF的法定使命，并被认为值得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来支持。

Subduction zones are sites of important chemical exchanges between the solid earth, hydrosphere and atmosphere. Seawater that penetrates into the subducting oceanic plate is incorporated in water-bearing minerals and carried deep into the earth. As the subducting plate descends and heats up, water is released and can influence the properties of subduction zone faults, the generation of subduction zone earthquakes, and the generation of magmas that feed arc volcanoes. Some of the water is released back into the atmosphere through volcanic eruptions. A critical unknown in this cycle is the amount and distribution of water in the incoming tectonic plate. How much water is stored in the plate? To what depth in the plate does water penetrate? Does the amount of water in the plate vary along the subduction zone? If so, what controls this variation? This project will use seismic and bathymetric (seafloor-depth) data collected across the Alaska subduction zone between Kodiak Island and the Shumagin Islands to constrain the volume and distribution of water stored in the subducting oceanic plate. The results will be valuable for understanding changes in the occurrence of large earthquakes and the compositions of magmas feeding volcanoes in this part of the Alaska subduction zone. Graduate and undergraduate students will participate in data analysis and gain valuable training.The volume and distribution of water is thought to control a host of fundamental processes at subduction zones, including megathrust behavior, the generation of arc magmas, and intermediate depth earthquakes. However, the amount of water delivered into the subduction zone by the incoming oceanic plate remains controversial and poorly known, resulting in great uncertainties in Earth’s deep water budget. In addition, the along-strike variation of water input, and its influence on along-strike variations in subduction processes, are also poorly constrained. Newly acquired seismic and bathymetric data from the Alaska Amphibious Community Seismic Experiment (AACSE) will be combined with existing data off the Alaska Peninsula to characterize outer-rise faulting and possible hydration throughout the incoming oceanic lithosphere. This subduction zone is an excellent target for study because it exhibits along-strike variations in megathrust coupling and seismicity at a range of depths, and existing data suggest along-strike variations in faulting and hydration. The lateral and depth distribution of hydrous phases in the incoming crust and mantle will be determined using seismic surface wave, body wave, and active source methods, and the results will be compared with incoming plate seismicity and mapped faults from bathymetry. Seismic anisotropy will provide constraints on the distribution of hydrated minerals around fault zones. The results will provide a comprehensive estimate of the incoming-plate water budget as a function of location along the Alaska subduction zone, allowing the effects of water on other subduction processes to be quantitatively evaluated. New constraints on the incoming water budget can be used by multidisciplinary studies evaluating the influence of water on megathrust and intermediate depth seismicity characteristics, along-strike volcanic output changes, and on the global mantle water budget. Estimates of the maximum size of incoming plate normal faults will allow the possible tsunami hazards of such earthquakes to be evaluated.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.