Collaborative Research: Understanding lithospheric structure and deformation in Alaska via integration of seismic imaging and geodynamic modeling

合作研究：通过地震成像和地球动力学建模的整合了解阿拉斯加的岩石圈结构和变形

• 批准号: 1829401
• 负责人: Karen Fischer
• 金额: $ 42.13万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-01 至 2022-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1829401&HistoricalAwards=false
• 关键词: Collaborative; Research; Understanding; lithospheric; structure

In the state of Alaska, the Earth's surface is moving at rates of 10's of millimeters per year with respect to the rest of the North American plate. This motion indicates that the Earth's lithosphere (the more rigid outer layer of the Earth that makes up the tectonic plates) is deforming. In southern Alaska, where the Pacific plate lithosphere is subducting beneath the North American plate, the North American plate is being compressed, for example creating the mountains of the Alaska Range. However, the forces that drive surface motion and North American plate deformation in the interior of Alaska are much less clear. The goal of this project is to measure the structure of the North American plate, in particular its thickness and its internal strength, and to model how forces acting on the edges and base of the plate are transmitted to the surface. The properties of the North American plate and the underlying mantle will be measured using surface and body waves that emanate from distant earthquakes and are recorded at sensors in Alaska, in particular the stations of the NSF Earthscope Transportable Array. The measured North American plate properties will be incorporated in numerical models that will explain motions observed at the surface in Alaska with the forces exerted on the North American plate by other plates and the motion of the deeper mantle. This work will improve understanding of the forces that drive motion and earthquakes on the Denali fault and other faults and that have created the mountains in Alaska. This project will contribute to the education of graduate and undergraduate students at Brown University and Purdue University.Deformation in Alaska manifests dramatic variations, from convergence and uplift in southern Alaska associated with subduction to more enigmatic deformation in interior Alaska that includes southward surface velocities. The drivers of this deformation and their relationship to underlying crust and mantle structure are debated and not yet understood. This project will address these questions by obtaining new models of the seismic structure of North American lithosphere and underlying asthenosphere beneath Alaska (using data from the NSF EarthScope Transportable Array and other networks). These constraints will be incorporated into 3D geodynamic modeling of the driving forces of upper plate deformation that explain observed surface deformation (as constrained by GPS, geologic and seismicity data). To accomplish this the project team will: (1) Carry out individual and joint analyses and inversions of converted body waves (Sp and Ps) and Rayleigh surface waves to obtain detailed models of crust and mantle shear velocity that robustly image mantle discontinuities. Attenuation and azimuthal anisotropy will also be determined; (2) Use shear velocity and attenuation to place bounds on temperature, bulk composition, grain size, water content and partial melt, and use these parameter ranges to place bounds on viscosity and density, incorporating viscosity constraints from dynamic modeling of observed surface motion; (3) Integrate models of viscosity and density with 3D geodynamic modeling of observed surface deformation and test geodynamic models with observations of azimuthal anisotropy in Rayleigh wave phase velocities and SKS splitting. The proposed work will improve understanding of the seismic structure of North American lithosphere and underlying asthenosphere; its implications for crust and mantle rheology and density; and the impact of upper plate and asthenosphere density and rheology on the rates and dynamics of upper plate deformation. A range of key questions will be addressed, including: (1) What processes enable the high rates of deformation and uplift observed in Alaska, and what is the role of upper plate rheology? How coupled are the lithosphere and asthenosphere and what are the impacts of tractions from asthenospheric flow at the base of the upper plate? (2) How has subduction modified the upper plate lithosphere? What are the effects of Yakutat terrane subduction, and does Yakutat mantle have distinct thermal or compositional properties that make it anomalous in terms of viscosity or buoyancy? What is the relationship of Yakutat terrane subduction and the Denali volcanic gap or the Wrangell volcanic field? (3) How do upper plate structure and tectonics relate north of the subduction zone? Where do offsets in upper plate properties occur across terrane boundaries and strike-slip faults? The project will contribute to the education and career development of graduate students at Brown and Purdue. At least one undergraduate will work on this project at Brown through the Leadership Alliance, a program that recruits students from groups underrepresented in STEM fields; one to two Brown undergraduates will also participate. The project will also reach a broader group of students and postdocs at Brown and Purdue through research group meetings and courses, and will be featured in outreach with elementary schools in Providence, RI.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.

在阿拉斯加州，相对于北美板块的其余部分，地球表面每年以10毫米的速率移动。 该运动表明地球的岩石圈（构成构造构造板的地球的更刚性外层）是变形的。 在阿拉斯加南部，太平洋板岩岩石圈在北美板块下方俯冲，北美板块被压缩，例如建立阿拉斯加山脉的山脉。 但是，在阿拉斯加内部驱动表面运动和北美板块变形的力尚不清楚。 该项目的目的是测量北美板块的结构，尤其是其厚度和内部强度，并建模如何作用在板的边缘和底部上的力传输到表面。 北美板块的性质和下面的地幔将使用从远处地震中散发出的表面和人体波测量，并记录在阿拉斯加的传感器上，尤其是NSF Earthscope可运输阵列的站点。 测得的北美板块特性将纳入数值模型中，这些模型将解释在阿拉斯加表面观察到的动作，而其他板块在北美板上施加的力以及更深的地幔的运动。 这项工作将提高人们对Denali断层和其他断层的运动和地震的力量的理解，并在阿拉斯加创造了山脉。 该项目将有助于布朗大学和普渡大学的毕业生和本科生的教育。阿拉斯加的新事物表现出巨大的变化，从与俯冲相关的阿拉斯加南部的融合和提升到包括南部表面速度在内的内部阿拉斯加更神秘的变形。 这种变形的驱动因素及其与潜在的地壳和地幔结构的关系尚未理解。该项目将通过获得阿拉斯加下面的北美岩石圈和基础运动层的新模型来解决这些问题（使用NSF EarthScope可运输阵列和其他网络的数据）。 这些约束将纳入上板变形的驱动力的3D地球动力学建模中，这些驱动力解释了观察到的表面变形（受GPS，地质和地震性数据的约束）。 为了实现这一目标，项目团队将：（1）对转换后的身体波（SP和PS）以及瑞利表面波进行个人和关节分析以及倒置，以获得牢固地图像地幔不连续性的地壳和地幔剪切速度的详细模型。还将确定衰减和方位角各向异性； （2）使用剪切速度和衰减将界限放在温度，散装组成，晶粒尺寸，水含量和部分熔体上，并使用这些参数范围在粘度和密度上限制界限，并结合了观察到的表面运动动态建模的粘度约束； （3）将观察到的表面变形和测试地球动力模型的3D地球动力学模型与瑞利波波相速度和SKS裂解中的方位角各向异性观察的3D地球动力学模型整合。拟议的工作将提高人们对北美岩石圈和基础软圈基础的地震结构的理解。它对地壳和地幔的风湿病和密度的影响；上板和小圈密度和流变学对上板变形的速率和动力学的影响。 将解决一系列关键问题，包括：（1）哪些过程使在阿拉斯加观察到的高变形和隆升速率以及上板流变学的作用是什么？ 岩石圈和动态圈的耦合方式如何，在上层板底部的软圈流量产生了什么影响？ （2）俯冲如何修饰上板岩石圈？ Yakutat地层俯冲的影响是什么，Yakutat地幔是否具有不同的热或组成特性，使其在粘度或浮力方面使其异常？ Yakutat Terrane俯冲与Denali火山缝隙或Wrangell火山场的关系是什么？ （3）上板结构和构造如何在俯冲带的北部关联？ 上板特性中的偏移发生在哪里发生跨地层边界和走滑断层？该项目将有助于布朗和普渡大学的研究生的教育和职业发展。至少有一个本科生将通过领导联盟在布朗（Brown）进行该项目，该计划从STEM领域中代表性不足的团体中招募学生；一到两个棕色的本科生也将参加。该项目还将通过研究小组会议和课程在Brown和Purdue的一组更广泛的学生和博士学位，并将在Providence的Providence与小学的外展活动中进行介绍，该奖项反映了NSF的法定任务，并认为通过基金会的知识分子和更广泛的影响，通过评估来评估CRITERIA，并被评估值得通过评估。

项目成果

Mapping the Lithosphere and Asthenosphere Beneath Alaska With Sp Converted Waves

• DOI: 10.1029/2022gc010517
• 发表时间: 2022-10
• 期刊: Geochemistry
• 影响因子: 3.7
• 作者: I. Gama;K. Fischer;J. Hua

A comparison of oceanic and continental mantle lithosphere

• DOI: 10.1016/j.pepi.2020.106600
• 发表时间: 2020-11
• 期刊: Physics of the Earth and Planetary Interiors
• 影响因子: 2.3
• 作者: K. Fischer;C. Rychert;C. Dalton;M. Miller;C. Beghein;D. Schutt

New Approaches to Multifrequency Sp Stacking Tested in the Anatolian Region

在安纳托利亚地区测试的多频 Sp 叠加新方法

• DOI: 10.1029/2020jb020313
• 发表时间: 2020
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Hua, J.;Fischer, K. M.;Wu, M.;Blom, N. A.
• 通讯作者: Blom, N. A.

Shear-wave velocity structure beneath Alaska from a Bayesian joint inversion of Sp receiver functions and Rayleigh wave phase velocities

来自 Sp 接收函数和瑞利波相速度的贝叶斯联合反演的阿拉斯加下方的剪切波速度结构

• DOI: 10.1016/j.epsl.2021.116785
• 发表时间: 2021
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Gama, Isabella;Fischer, Karen M.;Eilon, Zachary;Krueger, Hannah E.;Dalton, Colleen A.;Flesch, Lucy M.
• 通讯作者: Flesch, Lucy M.