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

使用实时海底大地测量数据确定卡斯卡迪亚巨型逆冲断层上倾端的锁定状态

• 批准号: 1825861
• 负责人: John Collins
• 金额: $ 16.82万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-01 至 2021-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1825861&HistoricalAwards=false
• 关键词: Determining; Locking; State; Updip; end

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.

由于地球构造板的运动在板块边界处运动，因此可以发生大地震和海啸，在板块边界上，海洋壳在上面的地壳下俯冲，例如卡斯卡迪亚（Cascadia），它是位于温哥华岛（或日本）附近美国西北部的近海。 导致这些地震的断层有时会从地壳深处一直到海底的地面破裂。发生这种情况时，海底的位移就会发生。而且，根据高潮的大小，这可能会产生巨阵。这样的例子将是2011年袭击日本的9级地震，并引起了一场大型海啸，摧毁了日本东北海岸的社区。但是，并非所有的俯冲破裂都会造成如此巨大的海啸，因为在某些情况下，位移沿着远低于海底的断层的部分局限。 这可以在2014年8.3智利智利地震中看到，该地震不会引起任何主要的海啸，因为地球上的大多数位移发生在10公里左右的深度。这项研究重点是收集和改善来自独特的子钻孔地球物理天文台中的卡斯卡迪亚地区的地震数据。这些数据用于研究卡斯卡迪亚地区的断层力学，并提供海啸危害预测。卡斯卡迪亚是一个有趣的领域，因为它靠近美国，并且是发生主动俯冲的地方，并且没有已知的大俯冲相关地震。重要的是要了解这种故障的“锁定”是否是真实的，因此引起了人们对积累压力正在积累并导致重大地震的担忧，或者是否通过一系列缓慢和低的滑动事件释放了压力。为了帮助了解卡斯卡迪亚地区的断层动态，2016年，在加拿大海洋网络电缆仪式天文台的温哥华岛附近的海底建立了独特的钻孔地球物理装置。这项研究校准并验证了从钻孔安装的数据流，以测试其可靠性，并从卡斯卡迪亚俯冲带的最浅水区提供实时的震荡和大地测量数据。 该新系统旨在对卡斯卡迪亚断层区浅层部分的破裂和特性特别敏感。这项工作的更广泛的影响包括在开发新装置的独特功能方面增加科学基础设施，并为地震提供与危险相关的重要数据，以及通过继续俯冲美国西北部和加拿大的海洋板所产生的潜在巨型海啸。它还代表了美国和加拿大科学家在加拿大海洋网络上的重要合作，以及来自NSF国际海洋发现计划的基础设施的杠杆式天文台。 2016年，美国和加拿大科学家和工程师的一支国际团队在加拿大电缆天文台的温哥华岛的卡斯卡迪亚俯冲区附近的海底安装了一个钻孔地球物理天文台。 自2017年以来，该系统一直在返回高质量，实时，地震和井眼倾斜数据。 传感器位于海底下方约300 m，在卡斯卡迪亚板边界断​​层上方约4公里处。对数据的初始分析表明，钻孔系统应该能够检测到低至4至4级的低幅度，缓慢的地震事件。但是，数据中仍有许多小信号和偏移仍有待研究，以确定其来源并确定仪器的稳定性及其数据的可靠性。这项研究继续改善流数据并确定其可靠性。 它涉及优化钻孔仪器，重点是改善脱水算法，在不同时间尺度上分类潜在的瞬态以及研究仪器的性能和稳定性。 这些活动可确保所有用户的最佳数据质量，从研究地震和海啸的实时警告系统的管理者到经理。来自钻孔天文台的数据也可用于检测和跟踪海洋哺乳动物，并提供有关气体水合物稳定性的信息。该工作还将确保收集的数据集在遥测中存在归档。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛的影响审查标准通过评估来获得支持的。

项目成果

A Lack of Dynamic Triggering of Slow Slip and Tremor Indicates That the Shallow Cascadia Megathrust Offshore Vancouver Island Is Likely Locked

缺乏慢滑和震颤的动态触发表明温哥华岛近海的卡斯卡迪亚浅层巨型逆冲断层很可能被锁定

• DOI: 10.1029/2018gl079519
• 发表时间: 2018
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: McGuire, Jeffrey J.;Collins, John A.;Davis, Earl;Becker, Keir;Heesemann, Martin
• 通讯作者: Heesemann, Martin