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: 2016062
• 负责人: Anne Becel
• 金额: $ 69.58万
• 依托单位: Columbia 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=2016062&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，俯冲带背景下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。在世界范围内，是什么控制了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。海水被进入的大洋板块带入俯冲带通常被用来解释板块界面滑动行为的变异性。然而，并入下沉的海洋板块的海水的体积和分布及其在不同俯冲带的深度的命运各不相同，由于现有观测的数量有限，人们对其知之甚少。墨西哥近海中美洲俯冲带的格雷罗断裂带及其邻近部分是世界上最著名的板块边界沿走向滑动变化的例子之一。格雷罗裂口100多年来没有发生过7级地震，但已知的最大的相对较浅的慢滑事件大约每4年发生一次，这种事件缓慢地释放能量，不会产生强烈的地震波。相比之下，邻近的部分在7级地震中破裂，似乎被强烈锁定。该项目将包括获取和分析Guerrero地震断裂带及其邻近段的海洋活源地震数据，以获得关于俯冲带断层的性质和几何形状的关键约束条件，包括进入的海洋板块和俯冲带内流体的丰度和分布。该项目的结果将有助于理解流体（如海水）在影响该边缘和类似俯冲带的对比滑动行为方面的作用。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2D广角地震反射/折射和超长偏移多通道地震（MCS）调查将在R/V Marcus G. Langseth上进行。该项目包括六个主要剖面，MCS和海底地震仪（OBS）数据将沿着这些剖面获取，另外的MCS剖面将在更大范围内扩展地震成像。对格雷罗裂口及其邻近段的研究将对两个核心问题产生独特的见解：(1)在中美洲俯冲带进入的年轻的缺乏沉积物的Cocos海洋板块的水化状态是什么，它如何沿走向变化并与俯冲带行为的变化有关？MCS成像和基于OBS和流数据的P波和S波速度模型，包括全波形反演以及射击和地震的联合反演，将提供在从脊轴向海沟轴俯冲之前以及在Guerrero Gap内外进入板块的水量和分布的初步估计。(2)俯冲板块和上覆板块的几何和物质性质如何影响逆冲断层的滑动行为？可控震源地震数据将对该俯冲带上部20-30公里的构造和性质，以及具有不同程度耦合和滑动行为的大型逆冲构造部分，带来新的、高分辨率的约束。这将有助于测试在其他俯冲带（如孔隙流体压力变化或断裂带非均质性变化）控制滑动行为的竞争性想法。要解决这一问题，需要综合考虑该项目对板块边界特性的限制，以及在Guerrero Gap内持续多年部署的大地测量和地震台站对滑动行为的研究结果。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。