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

俯冲带是固体地球、水圈和大气之间重要的化学交换场所。渗入俯冲洋板块的海水与含水矿物结合，被带到地球深处。随着俯冲板块的下降和升温，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，以及为弧火山提供岩浆的产生。一些水通过火山喷发被释放回大气中。在这个循环中，一个关键的未知因素是进入的构造板块中水的数量和分布。盘子里储存了多少水？水能穿透到板块的多深？板块内的水量沿俯冲带变化吗？如果是这样，是什么控制了这种变化？该项目将使用在Kodiak岛和Shumagin群岛之间的阿拉斯加俯冲带收集的地震和测深（海底深度）数据来限制俯冲海洋板块中储存的水的体积和分布。研究结果将有助于了解阿拉斯加俯冲带这一地区大地震发生的变化和岩浆构成。研究生和本科生将参与数据分析并获得宝贵的培训。水的体积和分布被认为控制着俯冲带的许多基本过程，包括大型逆冲行为、弧岩浆的产生和中深度地震。然而，进入的海洋板块向俯冲带输送的水量仍然存在争议，人们对其知之甚少，这导致地球深水预算存在很大的不确定性。此外，对水输入的沿向变化及其对俯冲过程中沿向变化的影响也知之甚少。阿拉斯加两栖社区地震实验（AACSE）新获得的地震和测深数据将与阿拉斯加半岛的现有数据相结合，以表征整个进入海洋岩石圈的外隆起断层和可能的水化作用。该俯冲带是一个很好的研究对象，因为它在一定深度范围内表现出大逆冲耦合和地震活动的沿走向变化，现有数据表明断层和水化作用的沿走向变化。利用地震面波、体波和活动震源等方法，确定了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性和测深断层图进行比较。地震各向异性将限制断裂带周围水合矿物的分布。研究结果将提供一个全面的估算，作为阿拉斯加俯冲带位置的函数，对进入板块的水预算进行估算，从而定量评估水对其他俯冲过程的影响。对来水收支的新约束可以用于多学科研究，以评估水对大逆冲和中深地震活动特征、沿走向火山输出变化以及全球地幔水收支的影响。对即将到来的板块正断层的最大大小的估计，将允许对这类地震可能造成的海啸危险进行评估。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。

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.