Constraining the relationship between orogenesis and seismogenesis along the southern Cascadia forearc

美国太平洋西北地区的造山活动沿其长度（加利福尼亚北部到美国-加拿大边境）显示出显著的变化。特别是，与俄勒冈州和华盛顿州的相同地区相比，海岸线和活火山系统之间的地区海拔最高，在加利福尼亚州最北端最广阔的地区（在纬度40 - 42度之间）。这可能是由于圣安地列斯断层系统北部和太平洋西北部的卡斯卡迪亚俯冲带之间复杂的相互作用造成的，后者可以产生7级地震，而卡斯卡迪亚俯冲带被认为可以产生9级地震。此外，相对较新发现的现象（间歇性震颤和缓慢滑动地震）在这部分边缘普遍存在，可能有助于造山，因此可能发生地震。该项目的目的是通过分析最近获得的数据集，从地球上部40英里的地下图像中创建的数据集，更好地了解卡斯卡迪亚前弧这部分的变形与造山、地震类型和成因之间的关系。了解加州北部这些不同地质特征之间的相互关系，并将其与俄勒冈州和华盛顿州北部观察到的情况进行比较，也可能为这些地区的灾害和造山过程提供见解。该团队还将与加州北部的当地社区合作，交流该地区的基本地质和构造背景；建立一个维基百科页面，让公众了解实验、项目目标和主要结果；并有助于培养研究生和本科生。俯冲边缘的构造和流变性质直接影响地震发生和覆岩板块变形，但有几个方面仍不清楚。研究小组将通过分析来自60个节点地震台站的新收集数据，研究南卡斯卡迪亚边缘（北加州）的组成、结构和地震特征如何对广泛的隆起、地形演化和高频率的间歇性震颤和滑动做出贡献。这些台站既有现有的，也有正在运行的地震台站。为了约束前弧的特征，该团队将采用稳健和新颖的地震方法，包括：1)远震接收函数成像，2)体波和表面波环境噪声干涉测量，3)接收函数和表面波色散测量的联合反演，以获得该地区新的三维剪切波速模型，以及4)震源机制分析。深入了解这些特征与南卡斯卡迪亚俯冲表现的关系，将有助于更好地理解是什么控制着卡斯卡迪亚边缘其他地区俯冲表现的变异性。此外，这些弧前地壳结构的高分辨率图像将使我们更好地了解可能的物理、成分和流变学控制的偶发性震颤和滑动过程。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。

Mountain building in the Pacific Northwest region of the United States of America shows significant variation along its length (northern California to the US-Canada border). In particular, the region between the coastline and the active volcanic system has the highest elevations over the broadest region in northernmost California (between 40 – 42 degrees latitude) compared to the same locations in Oregon and Washington State. This likely arises from the complex interactions between the northern portion of the San Andreas Fault System that can generate magnitude 7 earthquakes and the Cascadia Subduction Zone in the Pacific Northwest, thought to be able to generate magnitude 9 earthquakes. In addition, relatively newly-discovered phenomena (episodic tremor and slow slipping earthquakes) are prevalent in this portion of the margin, and may contribute to mountain building, and therefore earthquake potential. The purpose of this project is to better understand how deformation in this portion of the Cascadia forearc relates to mountain building and earthquake style and genesis by analyzing a recently acquired dataset created from subsurface images of the upper 40 miles of Earth. Understanding the interrelationships between these different geological characteristics in northern California and comparing them to what is observed further to the north in Oregon and Washington State, may also provide insights into the hazard and mountain building processes in those regions. The team will also engage with the local community in northern California to communicate the basic geologic and tectonic context of the region; develop a Wikipedia page to make the experiment, project goals, and major results accessible to the general public; and contribute to the training of graduate and undergraduate students.The structural and rheological properties of a subduction margin directly influence seismogenesis and overriding plate deformation, but several aspects remain poorly understood. The research team will investigate how the composition, structure, and seismic character of the southern Cascadia margin (northern California) contributes to broad uplift, topographic evolution, and high rates of episodic tremor-and-slip by analyzing newly-collected data from 60 nodal seismic stations with pre-existing and currently operating seismic stations. To constrain the characteristics of the forearc, the team will apply both robust and novel seismic methodologies, including: 1) teleseismic receiver function imaging, 2) body and surface wave ambient noise interferometry, 3) a joint inversion of receiver functions and surface wave dispersion measurements to obtain a new 3D shear-wave velocity model of the region, and 4) focal mechanism analysis. Insight into how these characteristics relate to the expression of subduction in southern Cascadia will then be used to better understand what controls variability in the manifestation of subduction elsewhere along the Cascadia margin. In addition, these high-resolution images of forearc crustal structure will allow for the better understanding of the possible physical, compositional, and rheological controls on the processes of episodic tremor-and-slip.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.