Characterization of the Oceanic Lithosphere-Asthenosphere Boundary in the Colombian Subduction Zone through Receiver Function Analysis

通过接收函数分析表征哥伦比亚俯冲带海洋岩石圈-软流圈边界

• 批准号: 2041631
• 负责人: Brandon Bishop
• 金额: $ 24.36万
• 依托单位: Saint Louis University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2041631&HistoricalAwards=false
• 关键词: Characterization; Oceanic; Lithosphere; Asthenosphere; Boundary

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).The goal of this project is to test two competing models of the boundary separating the Earth’s stiff outer layer (lithosphere) from the underlying, weaker layer (asthenosphere). One model proposes that this boundary is a narrow channel that decouples the lithosphere and asthenosphere. The other model proposes that this boundary forms a broad band of deformation that couples the lithosphere and asthenosphere. Each model has important implications for our understanding of plate tectonics—the process which drives the Earth’s long-term geologic evolution—and its relation to the Earth’s interior. Each model carries predictions about the boundary between the lithosphere and asthenosphere. These predictions can be tested using receiver functions. In collaboration with the Universidad Nacional de Colombia, this project uses recordings from seismic stations of the Colombian National Seismic Network located above the Colombian subduction zone. In this region, the characteristics of Nazca oceanic plate’s lower boundary can be examined over a range of depths to determine which of the models is most accurate. Understanding which model is most accurate will benefit society by helping to constrain the force balance acting on tectonic plates, especially around subduction zones where potentially destructive earthquakes driven by these forces occur. This project further benefits society by deepening international collaboration between institutions in the US and Colombia as well as furthering STEM education by providing training in seismology to a postdoctoral fellow.Observations of the oceanic lithosphere-asthenosphere boundary (LAB) support two categories of contradictory models for coupling between the lithosphere and underlying asthenosphere, and correspondingly contradictory implications for plate tectonics. One category interprets the boundary to be a narrow, melt-rich channel that decouples lithospheric plates from the asthenosphere. Plate motion is thus driven largely by slab pull. The other category interprets the boundary as a broad zone which couples plates to the asthenosphere. Plate motion is thus strongly influenced by asthenospheric flow induced drag. These models predict differing structures and localizations of shear along the LAB. Channel models predict two closely spaced, highly sheared boundaries while coupled models predict either a single boundary with little shear or a single highly sheared boundary. The predicted features respond differently to increasing pressure due to subduction. Channels narrow with depth and coupled structures persist to greater, differing depths, so observing a plate as it subducts offers an ideal natural experiment to test these models. Seismic waves with different frequency contents interact with these structures such that high frequencies can better image channels while low frequencies can better image coupled structures. This project uses P-to-S-wave receiver function analysis of radial and transverse components recorded at broadband seismic stations to examine structural characteristics and shear localization along the boundary. The complete characterization of structure and anisotropy caused by shear requires long-term observations at seismic stations from the coast to the back arc at a range of frequency bands. This project uses data from 2010 to the present from 26 stations in the Colombian National Seismic Network to investigate and characterize the subducting Nazca oceanic plate’s LAB from depths of 100 km at the coastline to 400 km in the back arc. These observations will provide constraints on the depth, thickness, and anisotropic properties (if present) of the boundary and use these to test the proposed models.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.

该奖项的全部或部分资金来源于《2021 年美国救援计划法案》（公法 117-2）。该项目的目标是测试将地球坚硬的外层（岩石圈）与地球坚硬的外层（岩石圈）分开的边界的两个相互竞争的模型。一种模型认为该边界是一条将岩石圈和软流圈分离的狭窄通道，另一种模型则认为该边界形成了一条耦合了岩石圈的变形带。每个模型都对我们理解板块构造（驱动地球长期地质演化的过程）及其与地球内部的关系具有重要意义。该项目与哥伦比亚国立大学合作，使用位于哥伦比亚俯冲带上方的哥伦比亚国家地震台网地震台的记录。在该区域，可以在一定深度范围内检查纳斯卡海洋板块下边界的特征，以确定哪个模型最准确。了解哪个模型最准确将有助于约束作用在构造板块上的力平衡，从而造福社会。特别是在这些力驱动的俯冲带附近，该项目通过深化美国和哥伦比亚机构之间的国际合作以及通过为博士后研究员提供地震学培训来进一步促进 STEM 教育，从而进一步造福社会。海洋岩石圈-软流圈边界（LAB）的研究支持两类关于岩石圈和底层软流圈之间耦合的矛盾模型，以及相应的对板块构造的矛盾含义，一类将边界解释为一条狭窄的、富含熔体的通道，使岩石圈解耦。因此，板块运动主要由板块拉力驱动。另一类将板块与软流圈耦合的边界解释为板块运动受到强烈影响。这些模型预测沿 LAB 的高度不同的结构和剪切局部化，而耦合模型则预测具有较小剪切力的单个边界或单个高剪切边界。与由于俯冲而导致的压力增加不同，通道随着深度而变窄，耦合结构持续到更大的不同深度，因此观察板块俯冲提供了一个理想的自然实验来测试这些模型的不同频率内容。对于这些结构，高频可以更好地成像通道，而低频可以更好地成像耦合结构。该项目使用宽带地震台记录的径向和横向分量的纵波接收函数分析来检查结构特征和剪切定位。要完整描述剪切力引起的结构和各向异性，需要对从海岸到弧后的地震台站进行一系列频段的长期观测。该项目使用 26 个台站的数据。哥伦比亚国家地震台网对从海岸线 100 公里深度到弧后 400 公里的俯冲纳斯卡海洋板块 LAB 进行调查和表征。这些观测结果将为深度、厚度和各向异性特性（如果存在）提供约束。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

A Thick, Sheared Zone at the Base of an Oceanic Plate: The Lithosphere-Asthenosphere Boundary of the Subducting Nazca Plate in Colombia as Revealed through P-to-S Receiver Functions

海洋板块底部厚厚的剪切带：通过 P-to-S 接收器函数揭示的哥伦比亚俯冲纳斯卡板块的岩石圈-软流圈边界

• 发表时间: 2022
• 期刊: AGU Fall Meeting
• 作者: Bishop, Brandon;Fernandez, Ademar;Warren, Linda M.;Pedraza, Patricia;Prieto, German A.;Dionicio, Viviana
• 通讯作者: Dionicio, Viviana

Receiver Function Derived Structural Constraints on Dynamic Processes Associated with the Young Nazca Lithosphere Subducting beneath Colombia

接收函数衍生的对与哥伦比亚下方俯冲的年轻纳斯卡岩石圈相关的动态过程的结构约束

• 发表时间: 2024
• 期刊: AGU Fall Meeting 2023
• 作者: Bishop, Brandon;Cho, Sung-Won;Warren, Linda M;Pedraza, Patricia;Prieto, German A;Dionicio, Viviana
• 通讯作者: Dionicio, Viviana