Collaborative Research: A new subsurface framework for the Cascadia subduction zone derived from integrated analyses of the CASIE21 long-offset multi-channel seismic experiment

太平洋西北部的卡斯卡迪亚俯冲区是一个国家利益重大、公众意识日益增强的地区，因为它有很高的地震和海啸风险。卡斯卡迪亚边缘记录的地震活动水平较低，这减少了对地震带的已知性质。该项目旨在确定卡斯卡迪亚边缘的结构和性质的变化，以更好地了解太平洋西北部的地震和海啸风险。这个项目将与其他小组合作，为边际建立一个新的3维图景。该项目将支持四名研究生、两名博士后研究人员和三名职业生涯早期的科学家。2021年6月1日至7月11日，作为卡斯卡迪亚地震成像实验(CASIE21)的一部分，使用R/V Marcus G.Langseth最先进的长偏移距能力收集了卡斯卡迪亚俯冲带的区域规模多通道地震研究。在这次考察中，在50-75公里的地震线网格中获得了5347公里的高质量12-15公里的流光数据，该网格横跨从北纬42°的戈尔达板块北部到温哥华岛近海俯冲结束的边缘，从形变前锋向海的50公里到海岸线附近。这项新的调查是在卡斯卡迪亚进行的第一次区域规模的研究，涵盖了俯冲带的大部分地区，填补了数据覆盖范围的重要空白。该项目利用CASIE21数据集来研究几乎整个卡斯卡迪亚边缘，并将在三个核心问题上产生独特的见解：(1)沿边缘的板块界面的几何形状是什么，发生显著的沉积物俯冲的地方，以及板块界面的属性，包括反射率和粗糙度，如何沿边缘和向下倾斜变化？板块界面性质如何与来水板块和上板块结构及大断裂断裂分段有关？(2)上板块的构造样式和演化如何沿走向变化，它们与大断裂强度、背板和流体运移的关系如何？(3)与弯曲断裂、海山分布和传播剪切带有关的来板块的岩石地层结构、最浅洋壳的结构、变形和水化潜力沿边缘变化，这些性质如何促进楔形演化和大断裂断裂分段？这项研究将导致根据地震图像作为主要产品，以及利用反射率、速度模型和应变分析进行精选研究，对近海卡斯卡迪亚地区进行新的区域尺度结构解释。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Cascadia Subduction Zone in the Pacific Northwest is a region of great national interest and growing public awareness because of its high earthquake and tsunami hazard. The Cascadia margin has low levels of recorded seismicity, which reduces what is known of the properties of the earthquake zone. This project aims to identify variations in the structure and properties of the Cascadia margin to better understand the earthquake and tsunami risk to the Pacific Northwest. This project will work with other groups to build a new 3-dimensional picture for the margin. The project will support for four graduate students, two postdoctoral researchers, and three early-career scientists.From June 1 to July 11, 2021, a regional-scale multi-channel seismic study of the Cascadia Subduction Zone was collected using the state-of-the-art long-offset capabilities of the R/V Marcus G. Langseth as part of the CAscadia Seismic Imaging Experiment 2021 (CASIE21). During the expedition, 5,347 km of high quality 12-15 km streamer data were acquired in a 50-75 km spaced grid of seismic lines spanning the margin from the northern Gorda plate at 42°N to the end of subduction offshore Vancouver Island and from ~50 km seaward of the deformation front to near the coastline. This new survey represents the first regional-scale study conducted at Cascadia, spanning most of the subduction zone and filling important gaps in data coverage. This project utilizes the CASIE21 dataset in order to study nearly the whole Cascadia margin and will yield unique insights into three core questions: (1) What is the geometry of the plate interface along the margin, where is significant sediment subduction occurring, and how do plate interface properties including reflectivity and roughness vary along the margin and down dip? How do plate interface properties relate to incoming plate and upper plate structure and megathrust rupture segmentation? (2) How do the structural style and evolution of the upper plate vary along strike and how are they related to megathrust strength, backstops, and fluid migration? (3) How does the lithostratigraphic architecture of the sediment section, and structure, deformation and hydration potential of the shallow-most oceanic crust of the incoming plate associated with bend faulting, distribution of seamounts and propagator shear zones vary along the margin and how do these properties contribute to wedge evolution and megathrust rupture segmentation? This study will result in construction of a new regional-scale structural interpretation of the offshore Cascadia region from seismic images as a primary product along with select studies making use of reflectivity, velocity models, and strain analysis.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.