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: 2140658
• 负责人: D. Randolph Watts
• 金额: $ 108.56万
• 依托单位: University of Rhode Island
• 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=2140658&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.

最大和最危险的地震是俯冲带地震，震源几乎完全在水下。地震的大小和造成巨大危险海啸的倾向是由板块界面耦合的变化决定的，板块界面耦合形成了断层的锁定和未锁定区域。了解板块耦合中的这些变化对于理解这些危险的地震至关重要。在偶尔发生的慢滑事件(SSE)中，应变沿着断层界面的一些离岸部分释放，其中断层的移动与正常地震相似，但存储的能量释放得如此缓慢，以至于这些事件在陆地上几乎检测不到。上交所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。有一些证据表明，板块界面一部分上的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到SSE，因为在SSE期间，海底向上移动，减小了压力计的深度。2015年，在新西兰近海拟议的研究区域使用压力计探测和绘制了SSE，因为这是目前适合在海上广泛应用的唯一可行方法。这些观测在很大程度上受到海洋涡流产生的海洋噪声的影响。现在计划在同一地区进行一项规模更大的实验。通过添加近海底流的海洋观测和垂直回声测深仪数据，研究应该表明，这种噪声源可以大大减少，从而更详细和更准确地揭示近海SSE的空间和时间范围，提高我们对与理解大地震相关的板块耦合的理解。该项目将培养一名研究生和博士后研究员，并让他们参与一个大型国际实验。在与新西兰和日本科学家的这项大型合作实验中，一大批海底大地测量、海洋和地震仪器将在新西兰北岛东海岸近海部署两年，预计在部署期间将在那里发生一个或多个浅层SSE。联合阵列将包括44个海底绝对压力计和12个海流计和向上俯视的声纳，以测试和开发消除水柱内产生的污染压力变化(标记为海洋噪声)的创新方法。低噪声海底数据将能够更准确地描述近海慢滑事件(SSE)的时空演变。将首次部署一个由11个APG传感器组成的阵列，该阵列配有一个系统，用于消除传感器数据的长期漂移，对海洋观测和以构造应变率应用海底垂直大地测量具有潜在的长期益处。来自组合阵列中的21个海底地震仪的数据将用于探索地震和震动与海底SSE之间的关系。这些观察将促进我们对俯冲区板块耦合的离岸变化的理解。这一裁决反映了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。