Collaborative Research: Behavior and structure on and around the megathrust revealed by the Alaska Amphibious Seismic Community Experiment

合作研究：阿拉斯加两栖地震社区实验揭示的巨型逆冲断层及其周围的行为和结构

• 批准号: 1947713
• 负责人: Emily Roland
• 金额: $ 22万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2021-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1947713&HistoricalAwards=false
• 关键词: Collaborative; Research; Behavior; structure; around

The planet’s largest earthquakes take place on subduction plate boundaries. These “megathrust” earthquakes, and the tsunamis they sometimes trigger, can cause extreme damage and loss of life in local and far-field communities. The Alaska Peninsula segment in particular hosted the second largest earthquake recorded anywhere and has been identified as a high-risk tsunami source for the west coast of North America. The Alaska megathrust also generates the most recorded earthquakes of any fault system in the U.S. In 2018-2019, the geophysical community deployed the first major shoreline-crossing seismic array off Alaska, placing 75 high-quality seismometers on the sea floor to complement several onshore synchronized deployments. This dataset, now openly available, provides the first comprehensive nearby sampling of signals from small to moderate earthquakes along the megathrust in Alaska. This project will analyze a range of earthquake-generated signals from this new dataset, to address questions such as: why are earthquakes more common in some places than others despite similar geology? where are the active faults in the region? and what is the nature of fault materials that allows earthquakes to be generated? The results will greatly improve the working models by which we understand the physics of earthquakes, of tsunami generation, and other related hazards. This project supports the training of graduate and undergraduate students.One of the best-known examples of along-strike variability of a megathrust is observed along the Alaska Peninsula. In a few hundred km, the plate interface varies from fully locked and capable of generating M9.2 earthquakes near Kodiak, to fully creeping near the Shumagin Islands. The fundamental controls on the rupture variability of megathrusts are poorly known, relevant to both along-strike variations as seen in Alaska, as well as updip/downdip changes that are seen along all subduction zones. A major new publicly available community seismic dataset has just been acquired along this segment of the Aleutian megathrust. The 15-month broadband dataset, termed the Alaska Amphibious Seismic Experiment, AACSE, provides extensive coverage far offshore and onshore of seismicity and structure, with uniform sampling. This project focuses on the megathrust sampled by the AACSE by characterizing and understanding the earthquake sources on it, the tremor produced along it, and by imaging the fine-scale structure using local-earthquake and teleseismic signals. Specifically, waveform-based methods will be used to greatly increase the quantity and precision of earthquake hypocenters along the megathrust, enabling characterization of along-strike variability. These will be complemented by studies of earthquake source properties to better understand spatial variation in rupture behavior, and to separate megathrust earthquakes showing upper plate and lower plate deformation. Modern tremor detection methods will be applied to the full dataset, to characterize any regions of downdip and potential updip tremor, and their along-strike variation. High-frequency mode-converted signals and autocorrelation of local-earthquake coda will be used to image the megathrust targeting spatial variations in its reflectivity strength and thickness; these analyses will be integrated with collocated receiver functions to generate a wide-band image of the plate boundary. This research will address several fundamental questions: Where is the plate boundary (as opposed to nearby regions in the upper and lower plate) seismogenic? How does the slip behavior and earthquake dynamics vary down-dip, and between locked and creeping sections? Do sharp boundaries in coupling correlate with strong variations in seismic behavior? How do earthquakes on the plate boundary relate to structure, and how does structure relate to dehydration or lithology? What explains the along-strike variability between locked and creeping sections? Do major potentially seismogenic splay faults exist in the upper plate? How is non-volcanic tremor related to regular earthquakes? The extensive amphibious array here allows an unprecedented opportunity to accurately resolve seismicity, tremor and structure in exactly the same place, with a variety of techniques, and in doing so provides an excellent opportunity to make progress on these issues.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.

地球上最大的地震发生在俯冲板块边界，这些“巨型逆冲断层”地震以及它们有时引发的海啸可能会对当地和远地社区造成极大的破坏和人员伤亡，尤其是阿拉斯加半岛地区发生了第二大地震。阿拉斯加巨型逆冲断层断层带是美国历史上记录最多的地震断层带，并已被确定为北美西海岸的高风险海啸源。 2018-2019 年，地球物理界在阿拉斯加附近部署了第一个主要的跨海岸线地震台阵，在海底放置了 75 个高质量地震仪，以补充多个陆上同步部署。该数据集现已公开，提供了首次全面的附近采样。阿拉斯加大型逆冲断层沿线的小到中度地震的信号该项目将分析来自这个新数据集的一系列地震产生的信号，以解决诸如以下问题：为什么地震在某些地方更常见。尽管地质条件相似，但该地区的活动断层在哪里？导致地震发生的断层物质的性质是什么？这些结果将极大地改善我们理解地震和海啸产生的物理模型。该项目支持研究生和本科生的培训。沿着阿拉斯加半岛观察到的沿走向变化的最著名的例子之一是，板块界面在数百公里范围内变化。完全锁定并能够生成科迪亚克附近的 M9.2 地震，到舒马金群岛附近的完全蠕动 对于巨型逆冲断层破裂变异的基本控制知之甚少，这与阿拉斯加所见的沿走向变化以及所见的上倾/下倾变化有关。刚刚沿着阿留申巨型逆冲断层的这一段获得了一个重要的新的公开社区地震数据集，称为阿拉斯加两栖地震数据集。地震实验 (AACSE) 通过统一采样，广泛覆盖远海和陆上的地震活动和结构。该项目重点关注 AACSE 采样的巨型逆冲断层，通过表征和了解其上的地震源、沿其产生的震动并通过成像。具体来说，将使用基于波形的方法来大大提高沿巨型逆冲断层的地震震源的数量和精度，从而能够表征地震。这些将通过地震源特性的研究来补充，以更好地了解破裂行为的空间变化，并将显示上部板块和下部板块变形的巨型逆冲地震分开，以将现代地震检测方法应用于完整的数据集。描述任何下倾和潜在上倾震颤的区域，及其沿走向变化的高频模式转换信号和局部地震尾波的自相关将用于对目标空间的巨型逆冲层进行成像。其反射率强度和厚度的变化；这些分析将与并置的接收器函数相结合，以生成板块边界的宽带图像。这项研究将解决几个基本问​​题：板块边界在哪里（而不是附近的区域）。上、下板块）地震发生过程中的滑移行为和地震动力学如何变化，以及锁定部分和蠕变部分之间的耦合边界是否与地震行为的强烈变化相关？ ，以及结构如何与脱水或岩性？如何解释锁定断层和蠕动断层之间的沿走向变化？上部板块中是否存在主要的潜在震源断层？这里广泛的两栖阵列如何与常规地震相关？使用多种技术在同一地点准确地解决地震活动、颤动和结构问题，这样做为在这些问题上取得进展提供了绝佳的机会。该奖项授予 NSF 的法定使命和通过使用基金会的智力价值和更广泛的影响审查标准进行评估，该项目被认为值得支持。