Collaborative Research: Meshed GNSS-Acoustic Array Design for Lower-Cost Dense Observation Fields

对海底变形的精确观测对于评估正在进行的地质过程及其造成的危害非常重要，包括最大的地震、海啸、海底火山活动、碳氢化合物变化和海底滑坡。目前，结合使用海面和海底仪器对一年或更长时间内发生的厘米级形变进行观测是昂贵的，特别是在使用大型研究船作为测量设计的一部分时。在这个项目中，该团队将使用一种相当新的但之前经过测试的自主绿色动力船来取代基于船舶的测量设计，比以前的方法降低测量成本一个数量级以上。为了进一步降低仪器成本并实现更广泛的应用，该项目将测试新的设计几何图形，这些几何图形有可能显著提高需要密集观测的能力。在这个项目中，一名博士后学者将被培养成下一代科学家和教育家。收集的数据将被贡献给社区数据档案，方法将被纳入社区软件进行研究。项目完成后，该仪器将成为美国国家科学基金会资助的现有仪器池的一部分，将深水观测能力从3000米增加到6000米，翻一番。用于这些行动的水面舰艇，商业上可以买到的波浪滑翔机，将配备天线，利用全球导航卫星系统(GNSS)进行自身定位。这艘船将在2024年和2025年夏季使用比美国仪表池目前可用的更低频率的声波信号来询问海底应答器的网状网络，以允许更深水作业所需的更大范围的测距。2024年，10个应答器阵列将沿着阿留申海沟的一段部署在4至6公里深的地方，将船只活动与现有的社区大地测量实验相结合，该实验只能延伸到3公里深。与每个观察点需要三个应答器的现有方法相比，共享转发器的密集网状网络设计可能会使仪器效率提高十倍，具体取决于几何结构。最后，该实验还将评估与俯冲带中常见的必然高梯度海底环境相关的潜在增加的误差。这种陡峭的测量同样适用于有可能发生破坏性海底山体滑坡的被动大陆斜坡。虽然设计实验测试了方法，但之所以选择这个地点，是因为人们对该地区断层的行为知之甚少。1946年的一场大地震在该地区引发了一场特大海啸。关于该地区持续断层行为的详细信息可以阐明该地区目前未知的机械耦合，为未来的地震奠定基础。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Precise observations of seafloor deformation is important for assessing ongoing geologic processes and the hazards they pose, including the largest earthquakes, tsunamis, submarine volcanism, hydrocarbon changes, and submarine landslides. Making observations of the centimeter-scale deformation that occurs over a year or longer using a combination of sea surface and seafloor instrumentation is currently expensive, particularly when using a large research vessel as a part of the measurement design. In this project, the team will use a rather new but previously tested autonomous, green-powered vessel that replaces the ship-based measurement design, reducing measurement costs by more than an order of magnitude over prior methods. To further reduce instrumentation costs and enable more broad use, the project will test new design geometries that have the potential to significantly increase capabilities where dense observations are needed. During this project, a postdoctoral scholar will be trained as a next-generation scientist and educator. The data collected will be contributed to a community data archive, and methods will be incorporated into community software for research. Following the project, the instrumentation will become a part of an existing NSF-funded instrument pool, doubling the capabilities for deep-water observations from 3000 to 6000 meters. The surface vessel for these operations, a commercially available Wave Glider, will be outfitted with antennas for positioning itself using Global Navigational Satellite Systems (GNSS). The vessel will interrogate a mesh-network of seafloor transponders during the summers of 2024 and 2025 using a lower frequency acoustic signal than currently available with the US instrument pool to allow for the extended ranging needed for deeper water operation. The 10-transponder array will be deployed between 4 and 6 km depth along a segment of the Aleutian trench in 2024, combining ship-activities with an existing community geodetic experiment, that can only extend to 3 km depth. The dense mesh-network design with the shared use of transponders could potentially allow for a ten-fold increase in instrumental efficiency, depending on geometry, over existing methods existing methods that require three transponders per observation point. Lastly, the experiment will additionally evaluate the potentially increased errors associated with necessarily high-gradient seafloor environments that are common in subduction zones. Such steep measurements could be similarly applied to passive continental slopes that have the potential for destructive submarine landslides. While the design experiment tests methodology, the location was chosen because little is known about the behavior of faults in the region, where a large earthquake in 1946 created an outsized tsunami. Detailed information about ongoing fault behavior in the region can illuminate the currently unknown mechanical coupling in the region that builds for future earthquakes.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.