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

美利坚合众国太平洋西北地区的造山活动沿其长度（加利福尼亚州北部至美加边境）表现出显着的变化。特别是，与俄勒冈州和华盛顿州的相同位置相比，海岸线和活火山系统之间的区域在加利福尼亚州最北端最广阔的区域（纬度 40 至 42 度之间）具有最高的海拔。这可能是由于圣安德烈亚斯断层系北部（可产生 7 级地震）与太平洋西北部卡斯卡迪亚俯冲带（据信可产生 9 级地震）之间复杂的相互作用所致。此外，相对较新发现的现象（阵发性震颤和慢滑地震）在边缘的这一部分很普遍，可能有助于造山，从而产生地震潜力。该项目的目的是通过分析最近获取的由地球上层 40 英里地下图像创建的数据集，更好地了解卡斯卡迪亚前弧部分的变形与造山、地震类型和成因之间的关系。了解加利福尼亚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，也可能有助于了解这些地区的灾害和造山过程。该团队还将与北加州当地社区合作，交流该地区的基本地质和构造背景；开发一个维基百科页面，使公众可以访问实验、项目目标和主要结果；俯冲边缘的结构和流变特性直接影响地震发生和上覆板块变形，但有几个方面仍知之甚少。研究小组将通过分析 60 个节点地震台站以及现有和当前运行的地震台站新收集的数据，研究卡斯卡迪亚边缘南部（加利福尼亚州北部）的成分、结构和地震特征如何导致广泛的隆起、地形演化和高频率的阵发性地震和滑动。为了限制弧前的特征，该团队将应用稳健且新颖的地震方法，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区域的新3D剪切波速度模型，以及4）震源机制分析。深入了解这些特征与卡斯卡迪亚南部俯冲表现的关系，将有助于更好地了解是什么控制着卡斯卡迪亚边缘其他地方俯冲表现的变异性。此外，这些前弧地壳结构的高分辨率图像将有助于更好地理解对阵发性震颤和滑动过程可能的物理、成分和流变控制。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。

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.