Collaborative Research: Assessing the State of Locking on the Frontal Thrust of the Cascadia Subduction Zone With Seafloor Geodesy

合作研究：利用海底大地测量评估卡斯卡迪亚俯冲带锋面逆冲锁定状态

• 批准号: 1657961
• 负责人: C. David Chadwell
• 金额: $ 42.06万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1657961&HistoricalAwards=false
• 关键词: Collaborative; Research; Assessing; State; Locking

The Cascadia Subduction Zone lies along the coast of Northern California, Oregon and Washington and is a significant geohazard that can generate great earthquakes and tsunamis. The Cascadia subduction zone is formed by the oceanic Juan de Fuca tectonic plate moving downward and beneath the overriding continental North American tectonic plate. The interface surface along which the two plates interact or rub is called the megathrust fault. As the Juan de Fuca plate moves downward, friction on the megathrust bends and contracts the overriding North American plate. The rate of buildup of strain is at the level of a centimeter or so per year, but eventually this stored energy is released causing a large earthquake and tsunami. The last great event occurred in 1700 and was powerful enough that the tsunami waves were recorded in Japan. Since that time the US Coast has become heavily populated posing a large hazard to society. Land-based GPS measurements can measure the slow accumulation of strain buildup, but the coastal sites are too far from the submerged shelf of the North American plate to provide reliable estimates far offshore. It is this offshore region where the tsunami generation may be greatest. This project uses GPS measured at the sea surface on a small robotic platform, combined with acoustic ranging from the platform to sensors on the seafloor. This technique is called GPS-Acoustic and can measure the centimeter-level motion of the seafloor. The project goal is to better document how much the seafloor is displacing and aid assessment of the potential size of the future tsunamis. This project will look for locking along the outer toe of the deformation front on the Cascadia Subduction Zone. Two new seafloor GPS-Acoustic sites at 43.0N and 45.3N will be added to the array of two recently established sites at 44.4N and 46.7N, and will allow for a determination of their motion relative to the North American plate. All of these sites are located several km inboard of the trench, and their motions will constrain the kinematics of the shallowest section of the frontal thrust. The project will use new lower cost methods that include GPS-Acoustic data that are collected from a Wave Glider rather than from an expensive ship. Permanent seafloor benchmarks will also be installed to extend the position time series indefinitely, and utilize commercial transponders that are reusable. Specifically, the re-purposing of seafloor transponders will be demonstrated by recovering and re-deploying an existing set of transponders. At the end of the three-year project, the six transponders at the two new sites will be recovered for reuse in future proposed projects of community interest. The benchmarks at these two new sites remain and can be re-occupied in the future (years to decades) to update the measurement time series. To interpret the motions inferred from the GPS-A observations, these offshore data will be integrated with existing onshore GPS and leveling observations, which will allow for a range of locking models to be explored. The project will also compare the four along-strike observations to each other, and correlate with along-strike variations in geologic and structural patterns.

卡斯卡迪亚俯冲带位于北加州，俄勒冈州和华盛顿的沿海，是一个重要的地质灾害，可以产生巨大的地震和海啸。 卡斯卡迪亚俯冲带是由海洋胡安·德福卡（Juan de Fuca）构造板向下和北美大陆构造板的下方形成的。 沿着两个板相互作用或摩擦的界面表面称为大型断层。 随着胡安·德·富卡板块向下移动，大型弯曲弯曲并收缩了北美板块。 应变的积累速率是每年厘米左右，但最终释放了这种储存的能量，导致大地震和海啸。 最后一个伟大的事件发生在1700年，足够强大，以至于在日本记录了海啸浪潮。 从那时起，美国沿岸人口稠密地对社会构成了巨大危害。 陆基的GPS测量值可以衡量应变累积的缓慢积累，但是沿海地区离北美板块的淹没架子太远，无法在海上提供可靠的估计值。 海啸一代可能是最大的海啸地区。 该项目使用在一个小型机器人平台上在海面测量的GP，结合了声学范围，从平台到海底传感器。该技术称为GPS声学，可以测量海底的厘米水平运动。 项目目标是更好地记录海底的数量，并评估未来海啸的潜在规模。该项目将寻找沿卡斯卡迪亚俯冲带的变形前脚趾锁定的。将在43.0N和45.3N处添加两个新的海底GPS声学位点，将两个最近在44.4N和46.7N的最近建立的地点的阵列添加到阵列中，并将允许确定其相对于北美板块的运动。所有这些地点都位于沟渠的几公里，它们的运动将限制额叶最浅的部分的运动学。 该项目将使用新的低成本方法，其中包括从波滑翔机收集的GPS声学数据，而不是从昂贵的船上收集的。也将安装永久的海底基准，以无限期地扩展位置时间序列，并利用可重复使用的商业发音器。具体而言，将通过恢复和重新部署一组现有的寄发器来证明海底发音器的重新修复。在为期三年项目结束时，将在未来提议的社区感兴趣的项目中回收两个新站点的六个应答器。这两个新站点的基准仍保留，并且可以在将来（数年数年）重新组成，以更新测量时间序列。 为了解释从GPS-A观测值推论的动作，这些离岸数据将与现有的陆上GPS和级别观测值集成在一起，这将允许探索一系列锁定模型。 该项目还将将四个沿撞击观测值与彼此进行比较，并与地质和结构模式的沿袭变化相关。