Determining the Locking State of the Updip end of the Cascadia Megathrust using Real Time Seafloor Geodetic data

在卡斯卡迪亚或日本等地，由于地球构造板块在板块边界的运动，海洋地壳被俯冲到上覆地壳之下，可能会发生大地震和海啸。卡斯卡迪亚位于美国西北部近海，靠近温哥华岛，或日本。引发这些地震的断层有时会从地壳深处一直破裂到海底表面。当这种情况发生时，海底就会发生位移；根据向上推力的大小，这可能会产生一场大海啸。一个这样的例子是2011年袭击日本的9级地震，那次地震引发了一场大海啸，摧毁了日本东北海岸的社区。然而，并不是所有的俯冲断裂都会产生如此大的海啸，因为在某些情况下，位移局限在远低于海底的部分断层上。这一点可以在2014年智利伊基克8.3级地震中看到，那次地震没有引发任何大海啸，因为地球上的大部分位移发生在大约10公里的深处。这项研究的重点是收集和改进卡斯卡迪亚地区的地震数据，这些数据来自一个独特的海底井下地球物理观测站。这些数据正被用于研究卡斯卡迪亚地区的断层力学，并提供海啸危险预报。卡斯卡迪亚是一个令人感兴趣的地区，因为它靠近美国，是一个正在发生活跃俯冲的地方，而且没有已知的与俯冲有关的大地震。重要的是要了解断层的这种“锁定”是否是真实的，从而引起人们的担忧，即累积的应力正在积累并导致大地震，或者应力是通过一系列缓慢和低滑动事件释放的。为了帮助了解卡斯卡迪亚地区的断层动力学，2016年在加拿大海洋网络有线天文台的温哥华岛附近的海底建立了一个独特的钻孔地球物理装置。这项研究校准和验证了从钻孔装置流出的数据，以测试其可靠性，并提供来自卡斯卡迪亚俯冲带最浅部分的实时地震和大地测量数据。这个新系统被设计成对卡斯卡迪亚断裂带浅部的破裂和性质特别敏感。这项工作的更广泛影响包括在开发这一新设施的独特能力方面增加科学基础设施，并提供与地震和潜在的巨型海啸相关的重要数据，这些数据是由美国和加拿大西北部的海洋板块继续俯冲产生的。这也代表了美国和加拿大科学家之间的重要合作，他们运营着加拿大海洋网络有线海底天文台，并利用了NSF国际海洋发现计划的基础设施。2016年，一个由美国和加拿大科学家和工程师组成的国际团队在加拿大有线天文台上，在温哥华岛近海卡斯卡迪亚俯冲带上倾端附近的海底安装了一个钻孔地球物理观测站。自2017年以来，该系统一直在返回高质量、实时的地震和井斜数据。传感器位于海底以下约300米，卡斯卡迪亚板块边界断层上方约4公里处。对数据的初步分析表明，钻孔系统应该能够探测到低震级、慢滑动、小至4级的地震事件。然而，数据中的许多小信号和漂移仍有待调查，以确定它们的来源，并确定仪器的稳定性和数据的可靠性。这项研究继续改进流数据并确定其可靠性。它包括优化钻孔仪器，重点是改进潮汐算法，对不同时间尺度的潜在瞬变进行编目，并调查仪器的性能和稳定性。这些活动确保了所有用户的最佳数据质量，从科学家到研究地震和海啸的实时警报系统的管理人员。钻孔观测站的数据还可用于探测和跟踪海洋哺乳动物，并提供有关天然气水合物稳定性的信息。这项工作还将确保在遥测发生故障时收集的数据集被存档。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。

Large earthquakes and tsunamis can occur due to the motion of Earth's tectonic plates at plate boundaries where oceanic crust is subducted under overlying crust in places such as Cascadia, which is offshore of the northwestern US near Vancouver Island, or Japan. Faults causing these earthquakes sometimes rupture from deep in Earth's crust all the way up to the surface of the seafloor. When that happens, displacement of the seafloor occurs; and, depending on the size of the up-thrust, this can generate a megatsunami. One such example would be the magnitude 9 earthquake that struck Japan in 2011 and generated a major tsunami that devastated communities along Japan's northeastern shore. Not all subduction ruptures, however, create such large tsunamis because, in some, displacements are confined along parts of faults that are well below the ocean floor. This can be seen in the 2014 magnitude 8.3 Chile Iquique earthquake which did not cause any major tsunami because most displacement in the Earth occurred at depths around 10 km. This research focuses on collecting and improving seismic data in the Cascadia region that is streaming from a unique subseafloor borehole geophysical observatory. These data are being used to study fault mechanics in the Cascadia area and provide tsunami hazard forecasts. Cascadia is an area of interest because it is close to the US and is a place where active subduction is occurring and for which there are no known large subduction-related earthquakes. It is important to understand if this "locking" of the fault is real, thus raising concern that accumulating stress is building up and result in a major earthquake or if the stress is being released through a series of slow and low, slip events. To help understand the fault dynamics in the Cascadia area, in 2016 a unique borehole geophysical installation was established in the seafloor off Vancouver Island on the Ocean Networks Canada cabled observatory. This research calibrates and validates data streaming from the borehole installation to test its reliability and provide real time-seismic and geodetic data from the shallowest part of the Cascadia subduction zone. This new system is designed to be especially sensitive to ruptures and properties in the shallow parts of the Cascadia fault zone. Broader impacts of the work include increasing infrastructure for science in terms of developing the unique capabilities of this new installation and providing important hazards-related data for earthquakes and potential mega tsunamis generated by continued subduction of the ocean plate under the northwest US and Canada. It also represents an important collaboration between the US and Canadian scientists running the Ocean Networks Canada cabled undersea observatory and the leveraging of infrastructure from the NSF International Ocean Discovery Program. In 2016, an international team of US and Canadian scientists and engineers installed a borehole geophysical observatory in the seafloor near the up-dip end of the Cascadia subduction zone offshore of Vancouver Island on the Canadian cabled observatory. Since 2017, this system has been returning high quality, real-time, seismic and borehole tilt data. Sensors are positioned about 300 m below the seafloor and about 4 km above the Cascadia plate boundary fault. Initial analysis of the data indicates the borehole system should be able to detect low magnitude, slow slip, earthquake events as small as magnitude 4. However, many small signals and excursions in the data still remain to be investigated to determine their sources and establish the stability of the instruments and the reliability of their data. This research continues the improvement of streaming data and determining its reliability. It involves optimizing the borehole instrumentation, with a focus on improving the de-tiding algorithm, cataloging potential transients at different time scales, and investigating instrument performance and stability. These activities ensure the best data quality for all users, ranging from scientists to managers of real-time warning systems who study earthquakes and tsunamis. Data from the borehole observatory can also be used to detect and track marine mammals and provide information on gas hydrate stability. The work will also ensure the dataset collected is archived if there are outages in telemetry.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.