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

合作研究：阿拉斯加巨型逆冲断层流体的海洋电磁勘探

• 批准号: 1654619
• 负责人: Robert Evans
• 金额: $ 18.11万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1654619&HistoricalAwards=false
• 关键词: Collaborative; Research; Marine; EM; Survey

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.

该项目的目的是在阿拉斯加半岛下方的深层断层内绘制水，在那里太平洋构造板块在北美构造板下方俯冲。被困在板之间的水被认为在控制板块边界的摩擦方面起着重要作用，并可以解释阿拉斯加半岛沿线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，以对沿板边界的沉积物和地壳中的水分布进行成像，以了解该关键区域中水的运输和释放如何调节地震行为和板块。该项目将推动电磁成像作为研究俯冲带的新工具，并有助于对大型断层关键区域中的流体体积进行成像。该项目支持海上本科生和研究生的培训，他们将学习如何收集和分析海洋电磁数据。本项目将使用新的海洋电磁技术（EM）成像技术来研究沿Semidi和Aleutian-Aleutian-Alaska-Alaska Alaska unduction unduction undcuction the Semidi和Shumagin sections沿Semidi和Shumagin section the Crust and Bastle的流体含量。俯冲系统的这些部分具有明显不同的海底织物，进入俯冲带和相应不同的地震性。来自该位置的2011年主动地震调查的数据表明，沿进气板的沉积物厚度和地壳破裂的变化，但无法完全限制流体的量和分布。将在一个月的160个海洋底站沿着三个沟通式横断面的轮廓和一个沿着撞击的轮廓收集被动和主动的EM数据。受控的源数据将对沉积物和地壳的电导率进行成像，而被动磁铁数据将映射深层地壳和上地幔电导率。这些数据一起将限制沟槽外层板的水合状态，沿着前臂下方的板面沿板界的分布，以及将流体释放到上覆的前臂外壳中。新的EM数据将与现有的地震调查结果一起解释为：（1）检验以下假设：沿着地震性和板块锁定的罢工变化与传入的海洋板的流体含量有关，这反过来又与板中的预先存在的结构以及对沟槽的织物的方向相关； （2）图像并量化从沿下部板的表面沉积物脱水释放的流体； （3）和量化过度压力的流体的图像和区域，以及与板上流体释放相关的压倒板的加热； （4）比较中美洲沟渠的阿留申 - 阿拉斯加俯冲区的电导率结构，这是一个由最终成员的系统进行的，在该系统中，海底故障与沟渠平行平行，有可能最大化该系统的流体液体。该奖项反映了NSF的法定任务，反映了通过评估的范围的范围，其构成师的范围是构成的范围。