Collaborative research: Quantifying incoming plate hydration and role of fluids on megathrust properties in and around the Guerrero Gap, offshore Mexico

合作研究：量化进入的板块水合作用以及流体对墨西哥近海格雷罗峡及其周围巨型逆冲断层特性的作用

• 批准号: 2016057
• 负责人: Donna Shillington
• 金额: $ 12.98万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-12-01 至 2024-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2016057&HistoricalAwards=false
• 关键词: Collaborative; research; Quantifying; incoming; plate

The plate boundary in subduction zone settings is known to exhibit a wide spectrum of behavior for how the two tectonic plates slide past each other. Many questions remain about what controls the wide spectrum of slip behavior within and between different subduction zone systems worldwide. Seawater delivered into the subduction zone by the incoming oceanic plate is commonly invoked to explain variability of plate interface slip behavior. However, the volume and distribution of seawater incorporated into the downgoing oceanic plate and its fate at depth vary between subduction zones and is poorly known owing to the limited amount of existing observations. The Guerrero Gap and neighboring segments at the Middle America subduction zone, offshore Mexico, is one of the best-known examples in the world of along-strike variations in slip behavior of the plate boundary. The Guerrero Gap has not ruptured in a M7 earthquake in more than 100 years but the largest known relatively shallow slow-slip events that release energy slowly without generating strong seismic waves occur approximately every 4 yrs. In contrast, the neighboring segments have ruptured in M7 earthquakes and appear to be strongly locked. This project will involve the acquisition and analysis of marine, active-source seismic data within the Guerrero Seismic Gap and neighboring segments in order to obtain critical constraints on the properties and geometry of the subduction zone faults, including the abundance and distribution of fluids in both the incoming oceanic plate and within the subduction zone. Results from this project will be valuable for understanding the role of fluids (e.g. seawater) in influencing the contrasting slip behavior both at this margin and similar subduction zones. This project will support two early career scientists and one pre-tenured scientist and will involve a strong collaboration between US, Mexican and Japanese scientists. The proposed study will also strongly complement an ongoing amphibious geodetic and seismic deployment led by Mexican and Japanese collaborators. A 47.5 day, combined 2D wide-angle seismic reflection/refraction and ultra-long offset multi-channel seismic (MCS) survey will be conducted onboard the R/V Marcus G. Langseth. This project includes six primary profiles along which both MCS and Ocean Bottom Seismometer (OBS) data will be acquired, and additional MCS profiles that extend seismic imaging over a larger extent of the margin. This study of the Guerrero Gap and neighboring segments will yield unique insights into two core questions: (1) What is the hydration state of the incoming, young sediment-starved Cocos oceanic plate at the Middle America subduction zone, and how does it vary along-strike and relate to changes in subduction zone behavior? MCS imaging and P and S- waves velocity models from OBS and streamer data, including full-waveform inversion as well as joint inversion of shots and earthquakes, will provide the first estimates of the amount and distribution of water in the incoming plate prior to subduction from the ridge axis to the trench axis and both in and outside of the Guerrero Gap, allowing us to examine the role of fluids in subduction zone processes and results will be compared the young but well-sedimented Cascadia and Nankai subducting plates, (2) How do geometrical and material properties of the subducting and overriding plates influence slip behavior along the megathrust fault? Controlled- source seismic data will bring new, high-resolution constraints on the architecture and properties of the upper 20-30 km of this subduction zone on parts of the megathrust that have different degrees of coupling and slip behavior. This will enable the testing of competing ideas for controls on slip behavior developed at other subduction zones, such as variations in pore-fluid pressure or fault zone heterogeneity. Addressing this question will require a synthesis of constraints on plate boundary properties from this project with results on slip behavior from an ongoing multi-year deployment of geodetic and seismic stations within the Guerrero Gap.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.

众所周知，俯冲带环境中的板块边界表现出两个构造板块如何相互滑动的广泛行为。关于是什么控制了全球不同俯冲带系统内部和之间的广泛滑动行为，仍然存在许多问题。进入大洋板块向俯冲带输送的海水通常被用来解释板块界面滑动行为的变异性。然而，由于现有观测量有限，不同俯冲带之间海水并入向下的大洋板块的体积和分布以及其在深处的去向各不相同，因此知之甚少。位于墨西哥近海的中美洲俯冲带的格雷罗缺口及其邻近的部分，是世界上最著名的板块边界滑动行为沿走向变化的例子之一。格雷罗缺口在100多年的M7级地震中没有破裂，但已知的最大的相对较浅的慢滑事件，缓慢释放能量而不产生强烈地震波，大约每4年发生一次。相比之下，邻近的地段在7级地震中破裂，似乎被强烈锁定。该项目将涉及采集和分析格雷罗地震空区和邻近地段内的海洋活跃源地震数据，以获得对俯冲带断层的性质和几何形状的关键制约，包括来水大洋板块和俯冲带内流体的丰度和分布。该项目的结果将对理解流体(例如海水)在影响该边缘和类似俯冲带的对比滑动行为中的作用是有价值的。该项目将支持两名早期职业科学家和一名终身科学家，并将涉及美国、墨西哥和日本科学家之间的强有力合作。拟议的研究还将有力地补充由墨西哥和日本的合作者领导的正在进行的两栖大地测量和地震部署。Marcus G.Langseth号上将进行为期47.5天的二维广角地震反射/折射和超长炮检距多道地震(MCS)联合调查。该项目包括六个主要剖面，沿这些剖面将采集MCS和海底地震仪(OBS)数据，以及附加的MCS剖面，这些剖面将地震成像扩展到更大范围的边缘。这项对格雷罗裂谷及其邻近部分的研究将对两个核心问题产生独特的见解：(1)在美国中部俯冲带，年轻的、缺乏沉积物的科科斯洋板块的水化状态是什么，它是如何沿走向变化的，并与俯冲带行为的变化有关？来自OBS和流光数据的MCS成像和P波和S波速度模型，包括全波形反演以及炮击和地震的联合反演，将提供对从山脊轴向海槽轴以及格雷罗裂隙内外俯冲之前传入板块中水的数量和分布的初步估计，从而使我们能够检查流体在俯冲带过程中的作用，并将结果与年轻但沉积良好的卡斯卡迪亚和南开俯冲板块进行比较；(2)俯冲和俯冲板块的几何和材料性质如何影响沿巨型逆冲断裂的滑动行为？可控源地震资料将对该俯冲带上部20-30公里具有不同耦合程度和滑动行为的部分地区的结构和性质带来新的、高分辨率的约束。这将使在其他俯冲带形成的控制滑动行为的相互竞争的想法得到测试，例如孔隙流体压力的变化或断裂带的非均质性。解决这个问题需要综合这个项目对板块边界属性的限制，以及格雷罗峡谷内持续多年部署大地测量站和地震站的滑移行为结果。该奖项反映了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。