Collaborative Research: Vertical seafloor geodesy to accurately image slow slip events in a noisy ocean environment

合作研究：垂直海底大地测量以准确成像嘈杂海洋环境中的慢滑事件

• 批准号: 2140657
• 负责人: Spahr Webb
• 金额: $ 138.24万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-02-01 至 2026-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2140657&HistoricalAwards=false
• 关键词: Collaborative; Research; Vertical; seafloor; geodesy

The largest and most dangerous earthquakes are subduction zone earthquakes where the source of the earthquake is almost completely underwater. The size of an earthquake and the propensity of an earthquake to create large dangerous tsunamis is determined by variations in the plate interface coupling which creates locked and unlocked regions of the fault. Understanding these variations in plate coupling is critical to understanding these dangerous earthquakes. Strain is released along some offshore parts of fault interfaces in occasional slow slip events (SSEs) where the fault moves much as with a normal earthquake, but the stored energy is released so slowly that these events are barely or not detectable on land. Regions between the SSE regions may remain locked, producing the potential for large tsunamigenic earthquakes. There is some evidence that SSEs on one part of a plate interface may increase strain on adjacent parts, triggering large earthquakes. Seafloor pressure gauges can detect SSEs as the seafloor moves upward during a SSE, decreasing the depth of the gauge. A SSE was detected and mapped in the proposed study region offshore New Zealand in 2015 using pressure gauges, as this is currently the only feasible method appropriate for wide application offshore. Those observations were greatly limited by the effects of oceanographic noise from ocean eddies. A much larger experiment is now planned for the same region. By adding oceanographic observations of near-seafloor current and vertical echo sounder data, the research should show this noise source can be much reduced and therefore reveal the spatial and temporal extent of offshore SSEs in greater detail and with better accuracy, improving our understanding of plate coupling relevant to understanding great earthquakes. The project will train a graduate student and postdoctoral researcher and involve them in a large international experiment. During this large collaborative experiment with New Zealand and Japanese scientists, a large array of ocean bottom geodetic, oceanographic, and seismological instruments will be deployed for two years offshore of the east coast of New Zealand's North Island, where one or more shallow SSEs are expected to occur during the deployment. The joint array would include 44 seafloor absolute pressure gauges (APGs) and 12 current meters and upward looking sonars to test and develop innovative methods to remove contaminating pressure variations that arise within the water column (labeled oceanographic noise). The reduced-noise seafloor data will enable more accurate description of the spatio-temporal evolution of offshore slow-slip events (SSEs). For the first time, an array of 11 APG sensors equipped with a system for removing long term drift from sensor data will be deployed, with potential long term benefit for oceanographic observations and for applying seafloor vertical geodesy at tectonic strain rates. Data from 21 ocean bottom seismometers in the combined array will be used to probe the relationship between earthquakes and tremor and seafloor SSEs. These observations will advance our understanding of offshore variations in plate coupling in subduction zones.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.

最大、最危险的地震是俯冲带地震，其震源几乎完全在水下。地震的规模和地震引发大型危险海啸的倾向是由板块界面耦合的变化决定的，板块界面耦合会产生断层的锁定和解锁区域。了解板块耦合的这些变化对于了解这些危险的地震至关重要。在偶尔发生的慢滑移事件（SSE）中，应变会沿着断层界面的一些近海部分释放，其中断层的移动与正常地震非常相似，但存储的能量释放得非常缓慢，以至于这些事件在陆地上几乎无法检测到。 SSE 区域之间的区域可能仍处于锁定状态，从而有可能引发大规模海啸地震。有证据表明，板块界面某一部分的 SSE 可能会增加相邻部分的应变，从而引发大地震。海底压力计可以检测 SSE，因为在 SSE 期间海底向上移动，从而减少了压力表的深度。 2015 年，使用压力计在新西兰近海拟议研究区域检测到了 SSE，并绘制了地图，因为这是目前适合在近海广泛应用的唯一可行方法。 这些观测结果受到海洋涡流海洋噪声影响的极大限制。现在计划在同一地区进行更大规模的实验。通过添加近海底流和垂直回声测深仪数据的海洋学观测，研究应该表明可以大大减少这种噪声源，从而更详细、更准确地揭示近海 SSE 的空间和时间范围，从而提高我们对板块的了解耦合与理解大地震有关。该项目将培养一名研究生和博士后研究员，并让他们参与大型国际实验。在与新西兰和日本科学家进行的这项大型合作实验中，将在新西兰北岛东海岸近海部署大量海底大地测量、海洋学和地震学仪器，为期两年，预计在那里会出现一个或多个浅层SSE在部署期间发生。 该联合阵列将包括 44 个海底绝对压力计 (APG) 和 12 个海流计以及仰视声纳，用于测试和开发创新方法，以消除水柱内出现的污染压力变化（标记为海洋噪声）。降噪海底数据将能够更准确地描述近海慢滑事件（SSE）的时空演化。将首次部署由 11 个 APG 传感器组成的阵列，配备消除传感器数据长期漂移的系统，这对海洋学观测和在构造应变率下应用海底垂直大地测量具有潜在的长期效益。组合阵列中 21 个海底地震仪的数据将用于探讨地震和颤动与海底 SSE 之间的关系。这些观察结果将增进我们对俯冲带板块耦合近海变化的理解。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。