Collaborative Research: Constraints on Interseismic Locking near the Trench on the Oregon Segment of the Cascadia Subduction Zone Using Seafloor Geodesy (GNSS-A)

该项目旨在测量横跨卡斯卡迪亚俯冲带的北美和胡安·德·富卡构造板块之间的相对运动，以帮助量化地震和海啸的危害。卡斯卡迪亚俯冲带是大地震和海啸的潜在震源，以两个构造板块交界处的一条大断层为代表。最近发生的大地震，比如2011年的东北地震，已经证明断裂可以延伸到令人惊讶的浅层深处，在那里海底的巨大垂直位移可以产生海啸。重要的是要了解卡斯卡迪亚俯冲带的情况是否类似，这增加了美国西海岸发生大海啸的危险。确定卡斯卡迪亚的海底是以俯冲板块的速度移动，还是因为断层被局部锁定而减慢了速度，这对断层力学的科学理解也很重要。技术上的挑战是在海底进行这些观察，海底既难以进入，又对仪器有腐蚀性。因此，这项工作需要专门的技术来进行必要的观察。本项目将支持培养一名海底大地测量技术的研究生和博士后，并将进一步发展推进海底大地测量所需的工程人力资源和基础设施。俄勒冈近海Cascadia俯冲带三个现有地点的海底基准时间序列将使用GNSS-Acoustic方法进行扩展。这些海底站点是在前几年建立的，对每个站点进行了不同数量的调查，得出了沿边缘的四个站点中的三个站点的构造板块速度的初步估计。在为期两年的项目中，将使用配备gnss声学的波浪滑翔机进行三次新的调查。与使用科考船相比，波浪滑翔机方法大大降低了调查成本。除了进行大地测量外，还将探索改进数据处理的新算法，包括旨在减轻水柱声速结构偏差的算法，以及利用多gnss数据的算法。最后，将使用弹性边界元模型推断海沟的运动学锁定量，目的是确定板块锁定是否沿走向变化，并与外部吸积棱镜的结构特征相关。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。

This project aims to measure the relative movement between the North American and Juan de Fuca tectonic plates across the Cascadia Subduction Zone to help quantify the earthquake and tsunami hazards. The Cascadia Subduction Zone, which is represented by a major fault at the interface of two tectonic plates, is a potential source of large earthquakes and tsunamis. Recent large earthquakes, such as the 2011 Tohoku earthquake, have demonstrated that rupture can extend to surprisingly shallow depths, where large vertical displacements of the seafloor can generate a tsunami. It is important to learn if the situation is similar on the Cascadia Subduction Zone, increasing the hazard from a large tsunami along the US west coast. Determining whether the seafloor in Cascadia moves at the subducting plate rate or is slowed because the fault is locked locally is also important to the scientific understanding of the fault mechanics. The technical challenge is to make these observations on the seafloor, which is both difficult to access and corrosive to instrumentation. Thus, this effort requires specialized techniques for making the necessary observations. This project will support the training of a graduate student and postdoctoral fellow in the use of seafloor geodetic techniques, and the project will further develop the engineering human resources and infrastructure needed to advance seafloor geodesy. The time series of seafloor benchmarks at three existing sites on the accretionary prism of the Cascadia Subduction Zone offshore Oregon will be extended using the GNSS-Acoustic method. These seafloor sites were established in previous years with varying numbers of surveys on each, yielding initial estimates of tectonic plate velocities at three of four sites along the margin. Three new surveys will be performed with a GNSS-Acoustic-equipped Wave Glider during the two-year project. The Wave Glider approach greatly reduces the survey cost compared to that undertaken with a research vessel. In addition to undertaking the geodetic surveys, new algorithms will be explored that improve the data processing, including algorithms designed to mitigate biases from the acoustic velocity structure of the water column and by capitalizing on multi-GNSS data. Finally, the amount of kinematic locking at the trench will be inferred using elastic boundary element models, with the goal to identify if plate locking varies along strike and correlates with structural features in the outer accretionary prism.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.