GeoPRISMS Postdoctoral Scholar: Refining GPS-Acoustic Processing to Measure Cascadia Subduction

GeoPRISMS 博士后学者：改进 GPS 声学处理以测量卡斯卡迪亚俯冲带

• 批准号: 1850685
• 负责人: David Schmidt
• 金额: $ 26.03万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-05-01 至 2022-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1850685&HistoricalAwards=false
• 关键词: GeoPRISMS; Postdoctoral; Scholar; Refining; GPS

There is geologic and historical evidence that a magnitude 9.0 earthquake, comparable in size to the earthquake off Japan in 2011, could strike the Cascadia subduction zone, the region immediately offshore Oregon and Washington State where the ocean floor is slowly crashing into and sinking below the North American continent. Normally when assessing seismic hazards on land, the movement of the ground is measured using the Global Positioning System (GPS), which informs where an earthquake may happen in the future and how large it may be. However, GPS can not be used in offshore regions like the Cascadia subduction zone because a seafloor instrument cannot directly communicate with an orbiting satellite through the water column. Instead, an analogous technique called GPS-Acoustic is used. GPS-Acoustic couples the satellite signals from GPS with sound waves from instruments deployed on the seabed to measure the movement of the seafloor. However, GPS-Acoustic instruments are not as accurate as onshore GPS stations because of difficulties in predicting how fast sound will travel through the ocean at any specific time and place. This project seeks to use improved oceanographic models of sound speed to improve measurements of seafloor movement along the Cascadia subduction zone. This will in turn allow a more accurate assessment of the seismic hazard in the region. Broader impacts of the work include the support of a postdoctoral scholar, potential improvements in subduction-zone seismic hazard assessments and potential cross-disciplinary impact for both geodesy and physical oceanography.The goal of the project is to test the assumptions of a stationary and horizontally layered sound velocity structure for GPS-Acoustic positioning. Oceanographic hindcast models will be used to inform a strategy to filter out the variations in sound velocity from the GPS-Acoustic residuals. This will allow implementation of methods to more accurately and efficiently isolate the geologic and oceanographic signal in the travel time residuals collected during GPS-Acoustic deployment. This approach will be evaluated using GPS and acoustic ranging data previously collected by a Wave Glider for sites above the Cascadia subduction zone. If successful, the accuracy of GPS-Acoustic displacement measurements will be improved from the cm-scale to the mm-scale, as well as the efficiency of GPS-Acoustic by shortening the required data collection window. With improved GPS-Acoustic measurements, refined boundary conditions will be generated for fault locking models along the Cascadia margin and aid in the monitoring of the seismic cycle, in line with the goals of the GeoPRISMS initiative to improve understanding of subduction cycles and deformation.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.

有地质和历史证据表明，一场规模与 2011 年日本近海地震相当的 9.0 级地震可能会袭击卡斯卡迪亚俯冲带，该地区紧邻俄勒冈州和华盛顿州近海，那里的海底正在缓慢地撞击并沉入海底。北美大陆。通常，在评估陆地地震危害时，会使用全球定位系统 (GPS) 测量地面的运动，从而得知未来可能发生地震的地点以及震级有多大。然而，GPS无法在卡斯卡迪亚俯冲带等近海地区使用，因为海底仪器无法通过水柱直接与轨道卫星通信。相反，使用了一种称为 GPS-Acoustic 的类似技术。 GPS-Acoustic 将 GPS 发出的卫星信号与部署在海底的仪器发出的声波耦合起来，以测量海底的运动。然而，GPS 声学仪器不如陆上 GPS 站准确，因为很难预测声音在任何特定时间和地点穿过海洋的速度。该项目旨在利用改进的声速海洋学模型来改进对卡斯卡迪亚俯冲带海底运动的测量。 这反过来又可以更准确地评估该地区的地震危险。这项工作的更广泛影响包括博士后学者的支持、俯冲带地震灾害评估的潜在改进以及对大地测量学和物理海洋学的潜在跨学科影响。该项目的目标是测试静止和水平的假设GPS声学定位的分层声速结构。 海洋学后报模型将用于制定从 GPS 声学残差中滤除声速变化的策略。 这将允许实施更准确、更有效地隔离 GPS 声学部署期间收集的行程时间残差中的地质和海洋信号的方法。 该方法将使用先前由波浪滑翔机收集的卡斯卡迪亚俯冲带上方地点的 GPS 和声学测距数据进行评估。如果成功，GPS声学位移测量的精度将从厘米级提高到毫米级，并且通过缩短所需的数据收集窗口来提高GPS声学的效率。 通过改进的 GPS 声学测量，将为沿着卡斯卡迪亚边缘的断层锁定模型生成精确的边界条件，并帮助监测地震周期，这符合 GeoPRISMS 计划的目标，以提高对俯冲周期和变形的理解。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。