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

位于太平洋西北部的卡斯卡迪亚俯冲带是一个具有重大国家利益和公众意识的地区，因为它的高地震和海啸危险。卡斯卡迪亚边缘有记录的地震活动水平较低，这降低了人们对地震带性质的了解。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，为边缘建立一个新的三维图像。该项目将支持四名研究生，两名博士后研究人员和三名早期职业科学家。2021年6月1日至7月11日，作为Cascadia地震成像实验2021 （CASIE21）的一部分，利用R/V Marcus G. Langseth号最先进的长偏移能力，对Cascadia俯冲带进行了区域尺度的多通道地震研究。在考察期间，在50-75公里间隔的地震线网格中获得了5,347公里的高质量12-15公里拖缆数据，这些地震线网格横跨从42°N的Gorda北部板块到温哥华岛近海俯冲结束的边缘，以及从变形前沿向海约50公里到海岸线附近。这项新的调查是在Cascadia进行的第一次区域尺度的研究，涵盖了大部分俯冲带，填补了数据覆盖的重要空白。该项目利用CASIE21数据集来研究几乎整个卡斯卡迪亚边缘，并将对三个核心问题产生独特的见解：(1)沿边缘的板块界面几何形状是什么，沉积物在哪里发生明显的俯冲，以及板块界面属性（包括反射率和粗糙度）沿边缘和向下倾角如何变化？板块界面性质如何与入板块和上板块构造以及大逆冲断裂分段有关？(2)上板块的构造样式和演化如何沿走向变化，与大逆冲强度、逆冲和流体运移有何关系？(3)与弯曲断裂、海山和传播剪切带的分布相关的沉积剖面的岩石地层构型、入陆板块最浅部洋壳的构造、变形和水化势如何沿边缘变化，以及这些性质如何影响楔形演化和大逆冲破裂分割？这项研究将以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的选择研究，为离岸卡斯卡迪亚地区建立一个新的区域尺度结构解释。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。

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.