Characterizing evolution and subduction of the Juan de Fuca plate: A joint inversion of ambient noise and air-gun shot data

俯冲带是地球上一个S构造板块被迫位于另一个构造板块之下的地方，是地球上最不为人所知的地区之一，但却给附近的海岸线和城市造成了重大危险。美国西海岸外相对较小的卡斯卡迪亚俯冲系统提供了一个独特的机会来研究大洋板块从形成到俯冲的结构和演化，以及恰好形成在近海的沉积楔形或弧前以及在俯冲板块上形成的火山弧的性质。拟议的项目旨在建立一个从地表通过地壳进入地幔岩石圈的3D高分辨率速度模型，从海沟延伸到弧形。具体地说，该项目将侧重于两个科学问题：(1)俯冲之前和之后大洋板块的结构是什么--板块结构是如何随时间演变的，以及俯冲之前大洋板块的水合程度如何？(2)来袭板块的结构与弧前结构中沿走向的变化之间有什么关系？一个分辨率良好的卡斯卡迪亚地震速度模型将有助于许多地质和地球物理研究，从而能够更好地定位地震和震源机制。该项目将支持一名职业生涯早期的女地球科学家的职业发展，她正在马萨斯大学阿默斯特分校建立一个新的地震学小组。该项目将支持本科生和研究生的培训。研究产品将纳入正在进行的地球科学公共宣传和入门课程。波传播模拟和地面运动地图是教育新英格兰公众了解地震危险的伟大工具。结果将通过Girls Inc.Eureka向服务不足的8-12年级女孩介绍！该计划是马萨诸塞州霍利奥克的Girls Inc.和UMASS之间基于STEM的强有力的合作。地震成像对俯冲板和上板块的几何和物理性质提供了强烈的约束。该项目将实施环境噪声和气枪射击的联合3D全波模拟和反演，以实现从地壳到最上地幔的高分辨率模型。将利用卡斯卡迪亚倡议海底地震仪和陆上宽带和短周期地震台的数据，包括两个活动震源地震试验的气枪射击。波传播模拟中的相移时间精度对浅层结构敏感，如沉积层和水柱，这将在本研究中考虑。将不同类型的地震数据联合反演成3D模型，将提供比单独数据集更高的海洋板块分辨率，并减少模型的不确定性。这个项目将产生一幅关于进入板块和弧前的清晰而完整的图片，这对于我们理解俯冲过程是必不可少的。更广泛地说，该项目对卡斯卡迪亚倡议社区实验的科学目标和推广做出了重大贡献。

Subduction zones where one of Earth?s tectonic plates is forced beneath another tectonic plate are one of the least understood regions on the planet and yet create major hazards for nearby coastlines and cities. The relatively small size of the Cascadia subduction system off the US west coast provides a unique opportunity to investigate the structure and evolution of the oceanic plate from its formation to subduction, as well as the nature of the sedimentary wedge or forearc that forms just offshore and the volcanic arc that forms on the over-riding plate. The proposed project aims to construct a 3D high-resolution velocity model from the surface through the crust into the mantle lithosphere, extending from trench to arc. Specifically, this project will focus on two scientific questions: (1) What is the structure of the oceanic plate prior to and after subduction - how does the plate structure evolve with time and how hydrated is the oceanic plate prior to subduction? (2) What are the relationships between the structure of the incoming plate and the along-strike variations in the forearc structure? A well-resolved Cascadia seismic velocity model will contribute to many geological and geophysical studies, allowing for better located earthquakes and source mechanisms. The project will support the career development of a female early-career geoscientist, who is in the process of establishing a new seismology group at UMASS-Amherst. The project will support training of undergraduate and graduate students. Research products will be integrated into ongoing public outreach and introductory classes in Earth Science. Wave propagation simulation and ground motion maps are great tools to educate the public in New England about seismic hazards. Results will be introduced to underserved 8th-12th grade girls through the Girls Inc. Eureka! Program, a strong STEM-based collaboration between Girls Inc. of Holyoke, Massachusetts and UMASS.Seismic imaging provides strong constraints on the geometry and physical properties of the subducting slab and the upper plate. The project will implement a joint 3D full-wave simulation and inversion of ambient noise and air-gun shots to achieve a model with high resolution from crust to uppermost mantle. Data from the Cascadia Initiative ocean bottom seismometers and onshore broadband and short-period seismic stations will be utilized, including air-gun shots of the two active-source seismic experiments. Accuracy of phase travel time in wave propagation simulation is sensitive to shallow structure, such as the sedimentary layers and water column, which will be taken into account in this study. The joint inversion of different types of seismic data into 3D models will provide a higher resolution of the oceanic plate with reduced model uncertainties than is possible with individual datasets. This project will produce a clear and complete picture of the incoming plate and forearc, which is essential for our understanding of the subduction process. More broadly, this project has very significant contribution to the scientific goals and outreach of the Cascadia Initiative community-based experiment.