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”地震，以及它们有时引发的海啸，会给当地和远地社区造成极大的破坏和生命损失。特别是阿拉斯加半岛部分发生了有记录以来的第二大地震，并被确定为北美西海岸的高风险海啸源。2018-2019年，地球物理学界在阿拉斯加附近部署了第一个主要的跨海岸线地震阵列，在海底放置了75个高质量的地震仪，以补充几个陆上同步部署。这个数据集现在可以公开获取，它提供了阿拉斯加巨型逆冲断层沿线小地震到中地震信号的第一个综合附近采样。这个项目将从这个新的数据集中分析一系列地震产生的信号，以解决这样的问题：尽管地质情况相似，为什么地震在某些地方比其他地方更常见？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？研究结果将极大地改进我们理解地震、海啸产生和其他相关灾害的物理原理的工作模型。该项目支持研究生和本科生的培养。大型逆冲断层沿走向变化的最著名的例子之一是在阿拉斯加半岛观察到的。在几百公里内，板块界面从在科迪亚克附近完全锁定并能产生9.2级地震，到在舒马金群岛附近完全蠕动。人们对大型逆冲断层破裂变异性的基本控制知之甚少，这既与阿拉斯加的沿走向变化有关，也与所有俯冲带的上倾/下倾变化有关。沿着阿留申大型逆冲断层的这一段，刚刚获得了一个重要的新的公开可用的社区地震数据集。这个为期15个月的宽带数据集，被称为阿拉斯加两栖地震实验（AACSE），通过统一的采样，提供了广泛的近海和陆上地震活动和结构的覆盖范围。本项目以AACSE采集的大逆冲断层为研究对象，对断层上的震源、沿断层产生的震动进行了表征和了解，并利用局地地震和远震信号对其精细结构进行了成像。具体而言，基于波形的方法将用于大大增加沿大逆冲断层地震震源的数量和精度，从而能够表征沿走向的变化。这些研究将辅以震源特性的研究，以更好地了解破裂行为的空间变化，并区分显示上板块和下板块变形的大逆冲地震。现代地震检测方法将应用于完整的数据集，以表征下倾和潜在上倾地震的任何区域及其沿走向的变化。利用高频模式转换信号和局地地震尾波的自相关特征对特大逆冲断层进行成像，定位其反射率强度和厚度的空间变化；这些分析将与配置的接收函数相结合，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（相对于上下板块附近的区域）在哪里发震？滑移行为和地震动力是如何变化的下倾，并在锁定和蠕动段之间？耦合中的尖锐边界是否与地震行为的强烈变化有关？板块边界上的地震与构造有何关系？构造又与脱水或岩性有何关系？如何解释锁定段和爬行段沿走向的变化？上板块是否存在主要的潜在发震断层？非火山性震颤与常规地震有何关系？这里广泛的两栖阵列提供了一个前所未有的机会，可以用各种技术精确地解决同一个地方的地震活动、震颤和结构，这样做为在这些问题上取得进展提供了一个极好的机会。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。