Structure and Hydration of the Explorer-Juan de Fuca-Gorda Plate System at the Onset of Subduction Beneath Cascadia

地震、海啸和火山爆发都是与俯冲带有关的地质灾害。了解俯冲带沿着的变异性对于控制北美这个人口稠密地区的地质灾害非常重要。该项目将分析从近海温哥华岛到俄勒冈州南部沿沿着卡斯卡迪亚边缘的海洋地震剖面。测量和分析将限制俯冲沉积厚度、下沉板块水量和沉积物-基底界面地形的变化。2021年，沿横跨卡斯卡迪亚边缘大部分长度的沿着剖面收集了一套现代和广泛的可控源地震数据集。沿沿着10个剖面的数据集由海底地震仪（OBSs）记录的同位超长拖缆多道地震反射和广角地震反射/折射数据组成。该项目将利用这些数据集模拟传入和下行板块以及增生棱柱体的沉积物、地壳和地幔的地震特性和结构。地壳和地幔岩石的断裂和蚀变引起地震速度的可检测变化，地震方法为评估板块水合作用提供了重要的遥感工具。研究人员将使用最先进的广角地震数据处理和成像方法，包括超长拖缆数据的向下延拓、超虚拟折射干涉测量以及拖缆和OBS数据的联合走时折射/反射层析成像，制作沿着每个OBS断面的P波和S波地震速度结构模型。地震速度模型将与有效介质理论一起使用，以约束壳幔孔隙度，以及传入和下行板块的流体和化学结合水的数量和分布。该项目的研究结果将对研究卡斯卡迪亚俯冲带过程的研究人员产生极大的兴趣，从变形前沿到弧下深度。该项目成果也将成为更新和改进美国地质调查局卡斯卡迪亚边际尺度三维地震速度模型的关键组成部分。该奖项反映了NSF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。

Earthquakes, tsunamis, and explosive volcanism are geohazards associated with subduction zones. Understanding the variability along the subduction zone is important for what controls geohazards in this populated region of North America. This project will analyze marine seismic profiles along the Cascadia margin from offshore Vancouver Island to southern Oregon. Measurements and analyses will constrain variability in subducting sediment thickness, amount of water in the downgoing plate, and topography of the sediment-basement interface. This project will contribute to the education of two graduate students by providing them support, data and training in geophysical imaging.In 2021, a suite of modern and extensive controlled-source seismic datasets was collected along profiles spanning most of the length of the Cascadia margin. The datasets along ten of the profiles consist of co-located ultralong-streamer multichannel seismic reflection and wide-angle seismic reflection/refraction data recorded in ocean bottom seismometers (OBSs). The project will use these datasets to model the seismic properties and structure of the sediments, crust and mantle of the incoming and down-going plates as well as those of the accretionary prism. Fracturing and alteration of crustal and mantle rocks give rise to detectable changes in seismic velocities, and seismic methods provide an important remote sensing tool for assessing plate hydration. The researchers will produce models of the P-wave and S-wave seismic velocity structure along each OBS transect using state-of-the-art wide-angle seismic data processing and imaging methods, including downward-continuation of ultra-long streamer data, super-virtual refraction interferometry, and joint travel-time refraction/reflection tomography of streamer and OBS data. The seismic velocity models will be used together with effective medium theory to constrain crust and mantle porosity, and the amount and distribution of fluid and chemically-bound water of the incoming and down-going plate. The findings from this project will be of great interest to researchers investigating Cascadia subduction zone processes, from the deformation front to sub-arc depths. The project results will also be a key component for updating and improving the U.S. Geological Survey’s margin-scale 3-D seismic velocity model for Cascadia.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.