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.

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。该项目的目标是测试将地球坚硬外层（岩石圈）与底层较弱层（软流圈）分开的两个相互竞争的边界模型。一种模型认为，这个边界是一个狭窄的通道，它将岩石圈和软流圈包围起来。另一种模式认为，这种边界形成了一个耦合岩石圈和软流圈的宽变形带。每一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有着重要的意义。每个模型都预测了岩石圈和软流圈之间的边界。这些预测可以使用接收器函数进行测试。该项目与哥伦比亚国立大学合作，利用哥伦比亚国家地震网位于哥伦比亚俯冲带上方的地震台站的记录。在这一地区，纳斯卡海洋板块下边界的特征可以在一定深度范围内进行检查，以确定哪种模型最准确。了解哪种模型最准确将有助于限制作用于构造板块的力平衡，特别是在俯冲带周围，这些力可能会导致破坏性地震。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）的观测支持了两类相互矛盾的岩石圈和下伏软流圈耦合模型，以及相应的对板块构造的相互矛盾的影响。一类解释边界是一个狭窄的，熔体丰富的通道，从软流圈的岩石圈板块。因此板块运动主要是由板块拉力驱动的。另一类则将边界解释为一个将板块与软流圈耦合起来的宽阔地带。因此，板块运动强烈地受到软流层流动引起的阻力的影响。这些模型预测不同的结构和局部剪切沿着LAB。通道模型预测两个紧密间隔，高度剪切的边界，而耦合模型预测一个单一的边界，几乎没有剪切或一个单一的高度剪切的边界。预测的功能不同的反应增加压力，由于俯冲。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。具有不同频率内容的地震波与这些结构相互作用，使得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。本项目使用P到S波接收函数分析的径向和横向分量记录在宽带地震台站，检查沿着边界的结构特征和剪切局部化。完整的结构和各向异性的特征所造成的剪切需要长期的观测地震台站从海岸到弧后在一系列的频带。该项目利用哥伦比亚国家地震台网26个台站2010年至今的数据，调查和描述纳斯卡俯冲海洋板块从海岸线100公里深处到弧后400公里深处的LAB。这些观测结果将提供边界的深度、厚度和各向异性特性（如果存在）的限制，并使用这些来测试拟议的模型。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。

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