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: 2128785
• 负责人: Emily Roland
• 金额: $ 22万
• 依托单位: Western Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-03-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2128785&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的边界上。这些“巨型逆冲断层”地震及其有时引发的海啸，可能在当地和远场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。在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，现在公开提供，提供了第一个全面的附近采样的信号，从小到中等地震沿着在阿拉斯加的巨型逆冲断层。该项目将分析来自这个新数据集的一系列地震生成信号，以解决诸如以下问题：为什么尽管地质相似，但地震在某些地方比其他地方更常见？这个地区的活断层在哪里？断层物质的性质又是什么呢？这些结果将极大地改善我们理解地震、海啸生成和其他相关灾害的物理学的工作模型。该项目支持研究生和本科生的培训。沿着阿拉斯加半岛观测到的大型逆冲断层沿走向变化的最著名例子之一。在几百公里的范围内，板块界面从完全锁定并能够在科迪亚克附近产生M9.2地震，到舒马金群岛附近完全蠕动。对巨型逆冲断层破裂变异性的基本控制知之甚少，与阿拉斯加所见的沿走向变化以及沿沿着所有俯冲带所见的上倾/下倾变化有关。沿着阿留申巨型逆冲断层的这一段，沿着刚刚获得了一个主要的新的公开可用的社区地震数据集。为期15个月的宽带数据集，称为阿拉斯加两栖地震实验，AACSE，提供了广泛的覆盖范围远离岸和岸上的地震活动和结构，统一的采样。该项目的重点是由AACSE采样的巨型逆冲断层，通过表征和了解其上的地震源，沿沿着它产生的震颤，并通过使用当地地震和地震信号对精细尺度结构进行成像。具体而言，将使用基于波形的方法来大大增加沿大逆冲断层沿着地震震源的数量和精度，从而能够表征沿走向的变化。这些将通过研究震源特性来补充，以更好地了解破裂行为的空间变化，并将显示上板块和下板块变形的巨型逆冲断层地震分开。现代震颤检测方法将应用于整个数据集，以表征任何下倾和潜在上倾震颤区域及其沿走向变化。将利用高频模式转换信号和当地地震尾波的自相关性，针对反射率强度和厚度的空间变化对巨型逆冲断层进行成像;这些分析将与配置的接收器功能相结合，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（相对于上下板块的附近地区）在哪里孕育地震？滑动特性和地震动力学在下倾以及锁定和蠕动段之间是如何变化的？耦合中的尖锐边界与地震行为的强烈变化相关吗？板块边界上的地震与构造有什么关系？构造又与脱水或岩性有什么关系？如何解释锁定段和蠕动段之间的沿走向变化？在上板块中是否存在潜在的主要地震展布断层？非火山性震颤与常规地震有何关系？广泛的水陆两栖阵列提供了一个前所未有的机会，可以准确地解决地震活动，震颤和结构在同一个地方，用各种技术，这样做提供了一个极好的机会，在这些问题上取得进展。这个奖项反映了NSF的法定使命，并已被认为是值得的支持，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。