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.

该项目的目标是绘制阿拉斯加半岛下的深断层内的水，太平洋构造板块正在向北美构造板块下方俯冲。被困在板块之间的水被认为在控制沿着板块边界的摩擦力方面起着重要作用，并且可以解释沿着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，以便对沉积物和地壳中水沿板块边界沿着的分布情况进行成像，目的是了解这一关键区域的水输送和释放如何调节地震行为和板块滑动。该项目将推进电磁成像作为研究俯冲带的新工具，并将有助于对巨型逆冲断层关键区域的流体体积进行成像。该项目支持对本科生和研究生进行海上培训，让他们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成像技术，研究阿留申-阿拉斯加俯冲带Semidi和Shumagin部分沿着地壳和地幔的流体含量。俯冲系统的这些部分在进入俯冲带海沟时具有显着不同的海底组构，并且地震活动也相应不同。2011年在该位置进行的主动地震勘探的数据显示，沉积物厚度和地壳断裂沿着进入板块的变化，但无法完全限制流体的数量和分布。将在为期一个月的巡航期间，在沿着三个跨沟剖面和一个沿走向剖面的160个海底站收集被动和主动EM数据。可控源电磁数据将绘制沉积物和地壳的电导率图，而被动大地电磁数据将绘制地壳深部和上地幔的电导率图。这些数据将共同制约在海沟外隆起处进入板块的水化状态、沿沿着前弧下板块界面的流体分布以及流体释放到上覆前弧地壳中。新的电磁数据将结合现有的地震勘测结果进行解释，以便：（1）检验以下假设：地震活动和板块锁定的沿着走向变化与进入的海洋板块的流体含量有关，而流体含量又与板块中预先存在的组构以及这种组构相对于海沟的方向有关;（2）成像和量化从沉积物脱水沿着下行板块的表面释放的流体;（3）成像和量化与从板片释放流体有关的上覆板块的超压流体和水力压裂的区域;（4）比较阿留申-阿拉斯加俯冲带的传导性结构与中美洲海沟的类似剖面，中美洲海沟是一个端元系统，海底断层平行于海沟排列，该奖项反映了NSF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。