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图，在那里太平洋构造板块被北美构造板块俯冲。被困在板块之间的水被认为在控制板块边界的摩擦中起着重要作用，并可能解释阿拉斯加半岛地震活动的巨大变化。本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分布，目的是了解水在这一关键区域的运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，并将有助于成像大型逆冲断层关键区域的流体体积。该项目支持本科生和研究生在海上的培训，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部分地壳和地幔的流体含量。这些俯冲系统剖面进入俯冲带海沟的海底构造明显不同，地震活动性也相应不同。2011年在该地点进行的一次活动地震调查数据显示，沉积物厚度和地壳破裂沿进入板块的变化，但不能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中收集，在160个海底站沿着三个海沟穿越剖面和一个沿走向剖面收集。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部和上地幔的电导率。这些数据将共同约束海沟外隆起处进入板块的水化状态，流体沿着弧前下方板块界面的分布，以及流体释放到上覆的弧前地壳中的情况。新的电磁数据将与现有的地震调查结果结合起来进行解释，以便：(1)验证地震活动性和板块锁定沿走向变化与进入大洋板块的流体含量有关的假设，而流体含量又与板块中预先存在的结构以及这种结构相对于海沟的方向有关；(2)对下沉板块表面沉积物脱水释放的流体进行成像和量化；(3)图像和量化超压流体区域以及与流体从板中释放相关的覆盖板的加氢加工；(4)将阿留申-阿拉斯加俯冲带的导电性结构与中美洲海沟的类似剖面进行比较，中美洲海沟是一个端元系统，海底断层与海沟平行排列，可能使进入该系统的流体通量最大化。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。

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.