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。渗透到俯冲的大洋板块的海水被结合在含水矿物中，并被带到地球深处。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，以及为弧形火山提供补给的岩浆的产生。一些水通过火山喷发释放回大气中。在这个周期中，一个关键的未知数是进入构造板块的水的数量和分布。盘子里储存了多少水？水在盘子里渗透到多深？板块中的水量是否随俯冲带而变化？如果是这样的话，是什么控制了这种变化？该项目将使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水深(海底深度)数据，以限制俯冲大洋板块中储存的水的数量和分布。这一结果将对了解阿拉斯加俯冲带这一部分大地震发生的变化和为火山提供燃料的岩浆的成分变化很有价值。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了俯冲带的一系列基本过程，包括大型逆冲行为、弧岩浆的产生和中等深度地震。然而，进入的大洋板块向俯冲带输送的水量仍然存在争议，而且鲜为人知，导致地球深水预算存在很大的不确定性。此外，水输入的沿走向变化及其对俯冲过程中沿走向变化的影响也受到较差的约束。来自阿拉斯加两栖社区地震实验(AACSE)的新获得的地震和水深数据将与阿拉斯加半岛外的现有数据相结合，以表征整个即将到来的大洋岩石圈的外隆断裂和可能的水化作用。这个俯冲带是一个很好的研究目标，因为它在一定深度范围内显示出巨型逆冲耦合和地震活动的沿走向变化，而且现有数据表明，断裂和水化作用沿走向变化。将利用地震面波、体波和活动源法确定来水地壳和地幔中含水相的横向和深度分布，并将其结果与来水板块地震活动和由水深测量绘制的断层图进行比较。地震各向异性将制约水合矿物在断裂带周围的分布。研究结果将对阿拉斯加俯冲带沿线位置的来水板块水收支进行综合估计，从而对水对其他俯冲过程的影响进行定量评估。对来水收支的新限制可用于多学科研究，评估水对巨型逆冲和中深度地震活动特征、沿走向的火山产出变化以及对全球地幔水资源收支的影响。对进入的板块正常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。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势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.