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对于两个构造板块如何相互滑过表现出广泛的行为。关于全球不同俯冲带系统内部和之间的广泛滑动行为的控制因素仍然存在许多问题。由传入的海洋板块输送到俯冲带的海水通常被用来解释板块界面滑移行为的变化。然而，纳入下降海洋板块的海水量和分布及其在深度的命运因俯冲带而异，并且由于现有观测数量有限，人们对此知之甚少。墨西哥近海中美洲俯冲带的格雷罗间隙和邻近部分是世界上板块边界滑动行为沿走向变化的最著名例子之一。格雷罗间隙已经有 100 多年没有在 M7 地震中破裂过，但已知最大的相对较浅的慢滑移事件大约每 4 年发生一次，该事件缓慢释放能量而不产生强烈的地震波。相比之下，邻近的路段在 M7 地震中发生破裂，并且似乎被牢固锁定。该项目将涉及格雷罗地震间隙和邻近段内海洋主动源地震数据的采集和分析，以获得对俯冲带断层的性质和几何形状的关键约束，包括俯冲带断层和俯冲带断层中流体的丰度和分布。进入的海洋板块和俯冲带内。该项目的结果对于理解流体（例如海水）在影响该边缘和类似俯冲带的对比滑移行为方面的作用非常有价值。该项目将支持两名早期职业科学家和一名准终身科学家，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合作者领导的正在进行的两栖大地测量和地震部署。为期 47.5 天的联合二维广角地震反射/折射和超长偏移多道地震 (MCS) 勘测将在 R/V Marcus G. Langseth 上进行。该项目包括六个主要剖面，将沿着这些剖面采集 MCS 和海底地震仪 (OBS) 数据，以及将地震成像扩展到更大范围边缘的附加 MCS 剖面。这项对格雷罗间隙和邻近部分的研究将对两个核心问题产生独特的见解：(1) 进入中美洲俯冲带的年轻、缺乏沉积物的科科斯洋板块的水合状态是什么，以及它是如何变化的- 撞击并与俯冲带行为的变化有关？ MCS 成像以及来自 OBS 和拖缆数据的 P 和 S 波速度模型，包括全波形反演以及炮弹和地震的联合反演，将提供俯冲之前传入板块中水量和分布的初步估计从山脊轴到海沟轴以及格雷罗间隙内外，使我们能够研究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进行比较俯冲板块，(2) 俯冲板块和俯冲板块的几何和材料特性如何影响沿着巨型逆冲断层的滑动行为？受控源地震数据将为具有不同程度耦合和滑移行为的巨型逆冲断层部分俯冲带上部 20-30 公里的结构和特性带来新的高分辨率约束。这将能够测试控制其他俯冲带滑动行为的竞争想法，例如孔隙流体压力或断层带异质性的变化。解决这个问题需要综合该项目对板块边界特性的约束，以及格雷罗峡内持续多年部署的大地测量和地震台站的滑移行为结果。该奖项反映了 NSF 的法定使命，并被认为是值得的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来提供支持。