Collaborative Research: Investigating Structure and Seismicity Within the Southern M9.2 1964 Great Alaska Earthquake Rupture Area Using a Dense Node Array

合作研究：使用密集节点阵列调查 1964 年 M9.2 大地震破裂区域南部的结构和地震活动

• 批准号: 2207441
• 负责人: Catherine Grace Barcheck
• 金额: $ 17.54万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2207441&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; Structure; Seismicity

A subduction zone is a region where an oceanic plate slips below a continental plate, along a shallowly inclined fault. One example is the Alaska-Aleutian subduction zone, which is responsible for more Magnitude 8 or greater earthquakes than any other subduction zone in the world, among them the 1964 Magnitude 9.2 Great Alaska Earthquake. Kodiak Island lies just above part of the Alaska-Aleutian subduction zone fault that was responsible for the 1964 earthquake, and in 2019, 400 seismic instruments were deployed there for 25 days as part of the Alaska Amphibious Community Seismic Experiment (AACSE). Using machine learning and other techniques, Worthington and her team will re-analyze data collected by these instruments to identify numerous very small earthquakes, and pinpoint their locations. This will provide an unprecedented snapshot of how earthquakes are distributed along the subduction zone fault and its vicinity. Recordings of these and other earthquakes will be used together to generate images of the subsurface, including the subduction zone fault itself, and to estimate physical properties of the fault and its surroundings. Detailed characterization of seismicity and structure within shallow subduction forearc regions offers insight into plate interface properties along the seismogenic megathrust, and the distribution, location and kinematics of active and past deformation. This project characterizes seismicity and structure beneath Qikertaq (Kodiak Island) using existing data from a densely-spaced seismic node array deployed along a ~50 km transect as part of the Alaska Amphibious Community Seismic Experiment (AACSE) in May, 2019. The Kodiak node array is located within the southern asperity of the largest historical US earthquake, the M9.2 1964 Great Alaska event, which ruptured a 600-800 km section of the Alaskan subduction zone. The main goals of the project are to determine: 1) The distribution of upper plate vs lower plate vs interface seismicity during the interseismic cycle through increased microseismicity (M1.0) detection and relocation; 2) The nature of the plate interface in the shallow forearc of the southern 1964 earthquake rupture asperity, properties of which control earthquake rupture, propagation and initiation; 3) Upper plate velocity structure within the Kodiak region, providing constraints on material strength and elastic properties of the seaward portion of the forearc. Using both machine-learning and coalescence-based automatic detection algorithms, this project will produce an enhanced seismicity catalog for the duration of the 25-day deployment. The locations of existing and new detections will be refined to provide a snapshot of the distribution of seismicity during the interseismic interval following great megathrust earthquakes. Travel-times from active-source marine shots and local earthquakes (including newly detected events) will be used for raytracing and inversion to develop a high-resolution velocity model of the shallow forearc above the plate interface. This velocity model will, in turn, be used to further refine event locations. Energy from local earthquakes will be used for imaging the crust and plate interface below the node array using scattered waves and reflected phases for vertical reflection profiling and coda auto-correlation.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.

俯冲带是大洋板块沿着一个浅倾斜的断层滑到大陆板块之下的区域。其中一个例子是阿拉斯加-阿留申俯冲带，该俯冲带比世界上任何其他俯冲带都要发生更多的8级或更大的地震，其中包括1964年的9.2级阿拉斯加大地震。科迪亚克岛位于1964年地震的阿拉斯加-阿留申俯冲带断层的一部分上方，2019年，作为阿拉斯加两栖社区地震实验（AACSE）的一部分，在那里部署了400台地震仪器，为期25天。利用机器学习和其他技术，沃辛顿和她的团队将重新分析这些仪器收集的数据，以识别许多非常小的地震，并确定它们的位置。这将提供一个前所未有的快照如何地震分布沿着俯冲带断层及其附近。这些地震和其他地震的记录将一起用于生成地下图像，包括俯冲带断层本身，并估计断层及其周围环境的物理特性。对浅俯冲弧前区域内地震活动和结构的详细描述提供了对沿孕震巨型逆冲断层沿着的板块界面性质、活动变形和过去变形的分布、位置和运动学的深入了解。该项目使用现有数据表征Qikertaq（科迪亚克岛）下方的地震活动性和结构，这些数据来自于2019年5月阿拉斯加两栖社区地震实验（AACSE）的一部分，沿沿着约50 km的横断面部署的密集地震节点阵列。科迪亚克节点阵列位于美国历史上最大的地震--1964年阿拉斯加大地震--的南部凹凸体内，该地震破坏了阿拉斯加俯冲带的600-800公里部分。该项目的主要目标是确定：1）通过增加微震活动，确定地震间周期中上板块与下板块与界面地震活动的分布（2）1964年南部地震破裂凸起浅弧前板块界面的性质，它控制着地震的破裂、传播和孕育; 3）科迪亚克区域内的上板块速度结构，对前弧向海部分的材料强度和弹性特性提供限制。使用机器学习和基于合并的自动检测算法，该项目将在25天的部署期间生成增强的地震活动目录。将对现有和新探测的位置进行改进，以提供大规模逆冲断层地震后地震间隔期间地震活动分布的快照。将利用活动源海洋炮点和当地地震（包括新探测到的地震）的走时进行射线追踪和反演，以建立一个高分辨率的板块界面上方浅弧前速度模型。这一速度模型又将用于进一步精确事件位置。来自当地地震的能量将被用于成像地壳和板块界面以下的节点阵列使用散射波和反射相位垂直反射剖面和尾波自相关。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。