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

最大和最危险的地震是震源几乎完全在水下的俯冲带地震。地震的大小和地震产生大型危险海啸的倾向是由板块界面耦合的变化决定的，这种耦合产生了断层的锁定和未锁定区域。了解这些板块耦合的变化对于了解这些危险的地震至关重要。在偶尔的慢滑事件（sse）中，断层会像普通地震一样移动，沿着断层界面的一些近海部分会释放应变，但储存的能量释放得很慢，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保持锁定状态，从而产生大海啸地震的可能性。有证据表明，在板块界面的某一部分发生的地震可能会增加相邻部分的应变，从而引发大地震。海底压力表可以探测到SSE，因为在SSE期间海底向上移动，减少了压力表的深度。2015年，在新西兰近海的拟议研究区域，使用压力表检测并绘制了SSE，因为这是目前唯一适用于海上广泛应用的可行方法。这些观测结果在很大程度上受到了来自海洋涡流的海洋学噪声的影响。一项规模更大的实验现在正计划在同一地区进行。通过增加近海底电流和垂直回声测深数据的海洋学观测，研究应该表明这种噪声源可以大大减少，从而更详细、更准确地揭示近海sse的时空范围，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一名博士后，并让他们参与一项大型国际实验。在这项与新西兰和日本科学家的大型合作实验中，将在新西兰北岛东海岸近海部署大量海底大地测量学、海洋学和地震学仪器，为期两年，预计在部署期间将发生一次或多次浅层地震。联合阵列将包括44个海底绝对压力表（apg）、12个海流计和向上看声纳，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）。降低噪声的海底数据将能够更准确地描述海上慢滑事件的时空演变。该项目将首次部署由11个APG传感器组成的阵列，这些传感器配备了一套系统，可以消除传感器数据中的长期漂移，这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效益。联合阵列中的21个海底地震仪的数据将用于探测地震、震颤和海底地震之间的关系。这些观察将促进我们对近海俯冲带板块耦合变化的理解。该奖项反映了美国国家科学基金会的法定使命，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。

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.