Collaborative Research: Marine EM Survey of Fluids in the Alaskan Megathrust

这个项目的目标是绘制阿拉斯加半岛下深断层内的水，在那里太平洋构造板块正被俯冲到北美构造板块之下。被困在板块之间的水被认为在控制板块边界的摩擦方面发挥了重要作用，并可能解释阿拉斯加半岛地震活动的巨大变化。这项研究将收集海底电磁地球物理数据，以成像沿板块边界的沉积物和地壳中的水的分布，目的是了解这一关键区域的水的传输和释放如何调节地震行为和板块滑动。该项目将推动电磁成像作为研究俯冲带的新工具，并将有助于成像巨型逆冲断层关键区域的流体体积。该项目支持在海上培训本科生和研究生，在那里他们将学习如何收集和分析海洋电磁数据。该项目将使用新的海洋电磁(EM)成像技术来研究阿留申-阿拉斯加俯冲带Semidi和Shumagin段沿线的地壳和地幔的流体含量。俯冲系统的这些部分进入俯冲带海沟的海底组构明显不同，地震活动也相应不同。2011年在该地区进行的一次活跃地震调查的数据显示，沿着进入的板块，沉积物厚度和地壳破裂程度不同，但无法完全限制流体的数量和分布。被动和主动电磁数据将在为期一个月的巡航期间收集，这些观测站位于160个海底观测站，沿着三个海沟交叉剖面和一个沿走向剖面。可控源电磁数据将成像沉积物和地壳的电导率，而被动大地电磁数据将绘制地壳深处和上地幔的电导率图。这些数据一起将限制进入的板块在海沟外隆起的水化状态，沿着前弧下的板块界面的流体分布，以及流体向上覆的前弧壳的释放。新的EM数据将结合现有的地震勘探结果进行解释，以：(1)检验地震活动和板块锁定沿走向的变化与进入的大洋板块的流体含量有关的假设，这反过来又与板块中预先存在的组构和该组构相对于海沟的方位有关；(2)沿下行板块表面的沉积物脱水释放的流体成像和量化；(3)与板块流体释放有关的超压流体和覆盖板块的水化作用区域的成像和量化；(4)将阿留申-阿拉斯加俯冲带的导电性结构与中美海沟的类似剖面进行比较，这是一个终端成员系统，其中海底断层平行于海沟排列，潜在地最大限度地增加了流入系统的流体流量。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。

The goal of this project is to map water inside deep faults beneath the Alaska Peninsula where the Pacific tectonic plate is being subducted underneath the North American tectonic plate. Water trapped between the plates is thought to play an important role in controlling friction along the plate boundary and may explain large variations in earthquake activity along the Alaska Peninsula. This study will collect seafloor electromagnetic geophysical data to image the distribution of water in the sediments and crust along the plate boundary, with the goal of understanding how the transport and release of water in this critical region may regulate earthquake behavior and plate slip. This project will advance electromagnetic imaging as a new tool for studying subduction zones, and one that will help to image fluid volumes in key areas of the megathrust fault. The project supports the training of undergraduate and graduate students at sea where they will learn how to collect and analyze marine electromagnetic data.This project will use new marine electromagnetic (EM) imaging technology to study the fluid content of the crust and mantle along the Semidi and Shumagin sections of the Aleutian-Alaska subduction zone. These sections of the subduction system have markedly different seafloor fabric entering the subduction zone trench and commensurately different seismicity. Data from a 2011 active seismic survey at this location show variations in sediment thickness and crustal fracturing along the incoming plate but are not able to fully constrain the amount and distribution of fluid. Passive and active EM data will be collected during a month-long cruise at 160 ocean-bottom stations along three trench-crossing profiles and one along-strike profile. Controlled-source EM data will image the electrical conductivity of the sediments and crust, while passive magnetotelluric data will map deep crustal and upper mantle conductivity. Together these data will constrain the hydration state of the incoming plate at the trench outer-rise, the distribution of fluids along the plate-interface beneath the forearc, and the release of fluids into the overlying forearc crust. The new EM data will be interpreted in conjunction with the existing seismic survey results to: (1) test the hypothesis that along strike variations in seismicity and plate locking are related to the fluid content of the incoming oceanic plate, which in turn is related to the pre-existing fabric in the plate and the orientation of this fabric with respect to the trench; (2) image and quantify fluids released from sediment dehydration along the surface of the down-going plate; (3) image and quantify zones of over-pressurized fluids and hydrofacturing of the overriding plate related to fluid release from the slab; (4) compare the conductivity structure at the Aleutian-Alaska subduction zone with a similar profile at the Middle America Trench, an end-member system where seafloor faults are aligned parallel to the trench, potentially maximizing fluid-flux into the system.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.