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.

在许多大陆与其相邻海底的边界上，海底构造板块在大陆构造板块之下滑动的过程中产生了应力。 当海底板块（有时被称为“下沉板块”）缓慢地俯冲到大陆下方（平均每年移动几英寸）时，沿边界的摩擦力沿着使两个板块发生弹性变形。 由这种机制积累起来的压力最终会在一次大的、潜在的毁灭性地震中释放出来。 这往往伴随着海啸-这一组合对许多沿海地区构成了重大危险，包括美国的太平洋西北部。虽然在陆地上使用永久性全球定位系统台站很容易观察到累积应力，但海底的变形却较难观察，因为全球定位系统使用的卫星信号无法穿透海水。 因此，必须使用其他手段来观察变形。该项目的目的是确定用一根长光纤电缆（最长100公里）连接一系列较短的传感光纤电缆来测量海底变形的可行性。 通过光纤发送的光可以检测到电缆中非常微小的长度变化。 如果小心地连接到海底，光纤电缆长度的变化表明底层材料的变形。 通过观测海底形变，研究人员希望有一天能够检测到近海地震引起的突然形变变化，并在相关震动到达陆地之前将信息传输到陆基网络，从而促进地震预警。该项目的技术方法已在小规模上得到验证。光纤，张紧之间的两个海底锚相隔几百米的干涉探测跟踪长度的变化。 光纤电缆一端的固态激光器将光注入光纤分束器。 部分光沿着伸展的光纤电缆传播到其远端的镜子，镜子将光反射回分束器。 激光的另一部分行进到在缠绕到固定玻璃心轴上的一段参考光纤的端部处的局部反射镜。 当两个反射光束在分束器处重新组合时，它们会发生干涉，产生波动的光级，可以处理这些光级以揭示纳米级的长度变化。 在这个项目中，将扩大既定方法，包括一系列连接到电缆的干涉传感器，电缆的长度可以覆盖整个大陆架，那里发生最危险的应力积累。 时分多路复用的方法被假定为能够探测沿着长电缆分布的十个应变传感器，从而充分扩展覆盖范围以监测100 km长剖面中的应变变化。 测试将在实验室中进行，测试适用于这些地球物理测量的光纤长度的时分复用方法。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。