Development of a Plate-scale Distributed Strain Sensing System: A Candidate for Earthquake Early Warning

板级分布式应变传感系统的开发：地震预警的候选系统

• 批准号: 2218876
• 负责人: Mark Zumberge
• 金额: $ 13.73万
• 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: 2022
• 资助国家: 美国
• 起止时间: 2022-10-01 至 2024-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2218876&HistoricalAwards=false
• 关键词: Development; Plate; scale; Distributed; Strain

On the boundary between many continents and their neighboring seafloors, stress builds up from the process in which the seafloor tectonic plate slides beneath the continental tectonic plate. As the seafloor plate (sometimes called the “downgoing slab”) is slowly subducted below the continent (moving at a few inches per year, on average), friction along the boundary causes both plates to elastically deform. The stress built up by this mechanism can ultimately be released in a large, potentially devasting earthquake. This is often accompanied by a tsunami – the combination poses a significant hazard to many coastal areas, including the Pacific northwest portion of the United States. While the built-up stress is readily observed on land using permanent GPS stations, deformation of the seafloor is more difficult to observe because the satellite signals used by GPS cannot penetrate seawater. Consequently, other means must be used to observe the deformation. The project aims to establish the feasibility of measuring deformation of the seafloor with a long optical fiber cable (up to 100 km) connected to a series of shorter, sensing optical fiber cables. Light sent through the optical fibers can detect very slight length changes in the cable. If carefully attached to the seafloor, changes in the length of the optical fiber cable indicate deformation in the underlying material. By observing seafloor deformation, researchers hope to one day be able to detect sudden deformation changes caused by an offshore earthquake and transmit the information to a land-based network faster than the associated shaking reaches land, facilitating an early-warning to the earthquake.The technical approach in this project has been demonstrated on a small scale. An optical fiber, tensioned between two seafloor anchors separated by a few hundred meters is interferometrically probed to track length changes. A solid state laser at one end of the optical fiber cable injects light into an optical fiber beamsplitter. Part of the light travels along the stretched optical fiber cable to a mirror at its far end, which reflects the light back towards the splitter. Another part of the laser light travels to a local mirror at the end of a length of reference optical fiber wound onto a fixed glass mandrel. When the two reflected light beams are recombined at the splitter, they interfere, creating fluctuating light levels that can be processed to reveal changes in length at the nanometer level. In this project, the established method will be expanded to include a series of interferometric sensors attached to a cable whose length could cover the entire continental shelf, where the most hazardous stress buildup occurs. The method of time-division multiplexing in postulated to be capable of probing ten strain sensors distributed along the long cable, thereby expanding coverage adequately to monitor strain changes in a 100 km long profile. The tests to be performed are to be done in the laboratory testing the time-division multiplexing approach in optical fiber lengths appropriate for these geophysical measurements.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.

在许多连续性及其附近海底之间的边界上，压力是由于海底构造板滑落在连续构造板下面的过程中所构成的。由于海底板（有时称为“下板”）缓慢地俯冲在大陆下方（平均每年几英寸移动），沿边界的摩擦会导致两个板弹性变形。这种机制所产生的压力最终可以在大型，可能破坏的地震中释放。这通常伴随着海啸 - 这种组合对包括美国太平洋西北地区在内的许多沿海地区构成了重大危害。虽然使用永久GPS站在陆地上很容易观察到积累的压力，但由于GPS使用的卫星信号无法渗透海水，因此海底的变形更难观察到。因此，必须使用其他手段来观察变形。该项目的目的是建立用长的光纤电缆（最高100 km）连接到一系列短的，感应光纤电缆的长光纤电缆（最高100 km）的海底变形的可行性。通过光纤发送的光可以检测到电缆的略长时间变化。如果小心地连接到海底，光纤电缆的长度的变化表示下面的材料中的变形。通过观察海底变形，研究人员希望有一天能够检测到由海上地震引起的突然变形变化，并将信息传输到陆地网络中，比相关的摇动更快地传输到陆地网络，从而支持早期进行地震。在两个海底锚之间张紧了几百米的光纤，经过探测以跟踪长度变化。光纤电缆一端的固态激光器将光注射到光纤束弹刀中。一部分光线沿着拉伸的光纤电缆在其远端向镜子传播，这将光反射回分离器。激光灯的另一部分在长度参考光纤滚动到固定玻璃曼德斯的末端的本地镜子上。当两个反射的光束在分离器上重新组合时，它们会干扰，从而产生波动的光级，可以处理以揭示纳米水平的长度变化。在这个项目中，将扩展的方法将扩展到一系列连接到电缆上的干涉量传感器，其长度可以覆盖整个连续的架子，并在此构成最危险的应力积累。假定的时间分割多路复用方法，该方法能够探测沿长电缆分布的十个应变传感器，从而适当扩展覆盖范围，以监测100 km长轮廓的应变变化。要进行的测试将在实验室测试中进行，以适合这些地球物理测量的光纤长度的时间划分多路复用方法进行。该奖项反映了NSF的法定任务，并被认为是通过基金会的知识分子优点和更广泛影响的审查标准通过评估来评估的。