Geodetic Characterization of the Easternmost Alaska Subduction Zone

阿拉斯加俯冲带最东端的大地测量特征

• 批准号: 2137618
• 负责人: Julie Elliott
• 金额: $ 22.64万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-05-15 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2137618&HistoricalAwards=false
• 关键词: Geodetic; Characterization; Easternmost; Alaska; Subduction

Non-Technical SummarySubduction zones, where one tectonic plate descends beneath another, produce great earthquakes and thus pose significant seismic hazards. Understanding the characteristics of the plates, such as the geometry of the descending plate (or slab), and the processes by which they slip past each other is key to assessing the extent of the seismic risk. Parts or all of the two plates may be stuck together, accumulating strain that may be released in a large earthquake, or they may slide past each other more quietly, including in "slow slip events", where energy is released over days or years instead of seconds.South central Alaska is an excellent laboratory for investigating links between slab and upper plate characteristics and slip behavior in subduction zones. The region generated the second-largest earthquake ever recorded (a magnitude 9.2 in 1964), but major questions remain about processes along this margin. Earthquake activity shows that the Alaska-Aleutian slab is subducting beneath part of southern Alaska. This earthquake activity stops abruptly to the east of where the magnitude 9.2 earthquake occurred, leading to speculation that the slab may not be continuous throughout the area. Recent GPS studies have suggested that the slab is present and locked with the upper plate across much of the area and seismic investigations have found evidence that transient behavior may also occur, but sparse data has limited further work.The project team, from Purdue University, is installing four new continuous GPS sites and five temporary GPS sites. The team is combining data from these sites with data from existing sites to investigate subduction processes in the area, including understanding the geometries of the slab and upper plate and determining where, and to what degree, the plates are locked. The team is also searching for subtle evidence of transient events; if found, those events can be related to plate geometries and plate locking. The project is also providing local K-12 teachers the opportunity to participate in fieldwork and learn about how GPS data is used in tectonic studies. Lesson plans developed with these teachers incorporate this project's research into a larger scale view of the region's tectonics and give students experience working with scientific data. The team is spreading its research results to a larger audience through interactions with National Park Service staff and public lectures. Overall, this project is generating and communicating a more complete understanding of processes in the easternmost Alaska subduction zone, which will improve seismic hazard estimates.Technical DescriptionThis proposal seeks to improve understanding of the relationship between complicated slab geometries (e.g. flat slab subduction, edges or kinks in slabs) and subduction-related processes such as upper plate deformation, coupling along the subduction interface, and transient events (e.g. slow-slip). Data from 4 new continuous GPS sites, 5 new campaign sites, and existing continuous and campaign sites in the region are being used to examine strain patterns, the geometry of the subducting slab, coupling along the subduction interface, upper plate motion, and transient processes along the easternmost Alaska subduction zone. The project is addressing the following questions: 1) What is the geometry of the subduction interface? Where is the eastern edge of the active subduction interface? How does this relate to the Wrangell Volcanic field and observed seismicity? 2) How does coupling vary within the easternmost Alaska subduction zone? Where does the transition from locked to creeping occur? How does this relate to the observed tremor, upper plate deformation, and seismicity? 3) Are there transient events resembling slow-slip events on the subduction interface? How do these transient events relate to the interface geometry and coupling distribution? The new data are allowing an assessment of plate boundary characteristics on a much more spatially and temporally dense scale than currently possible, leading to more detailed and realistic models of the behavior of the Yakutat slab interface and its influence of the region's tectonics.

非技术摘要俯冲带，即一个构造板块下降到另一个构造板块下方的区域，会产生大地震，从而造成严重的地震危险。 了解板块的特征，例如下降板块（或板块）的几何形状，以及它们相互滑过的过程，是评估地震风险程度的关键。 两个板块的部分或全部可能粘在一起，积累在大地震中可能释放的应变，或者它们可能更安静地相互滑过，包括在“慢滑事件”中，其中能量在几天或几年内释放阿拉斯加中南部是研究板块和上板块特征以及俯冲带滑移行为之间联系的优秀实验室。该地区发生了有记录以来第二大地震（1964 年震级为 9.2 级），但沿这一边缘的过程仍然存在重大问题。 地震活动表明阿拉斯加-阿留申板块正在俯冲到阿拉斯加南部部分地区下方。 此次地震活动在 9.2 级地震发生地以东突然停止，导致人们猜测该板块可能在整个地区并不连续。 最近的 GPS 研究表明，该板块存在并与大部分区域的上板块锁定，地震调查发现也可能发生瞬态行为的证据，但稀疏的数据限制了进一步的工作。来自普渡大学的项目团队，正在安装四个新的连续 GPS 站点和五个临时 GPS 站点。 该团队正在将这些地点的数据与现有地点的数据相结合，以调查该地区的俯冲过程，包括了解板块和上板块的几何形状，并确定板块被锁定的位置和程度。 该团队还在寻找短暂事件的微妙证据；如果发现，这些事件可能与板几何形状和板锁定有关。 该项目还为当地 K-12 教师提供参与实地考察和了解 GPS 数据如何用于构造研究的机会。 与这些教师一起制定的课程计划将该项目的研究纳入该地区构造的更大规模视图中，并为学生提供使用科学数据的经验。 该团队正在通过与国家公园管理局工作人员的互动和公开讲座向更多受众传播其研究成果。 总体而言，该项目正在对阿拉斯加最东部俯冲带的过程产生并交流更全面的了解，这将改善地震灾害估计。技术描述该提案旨在提高对复杂板片几何形状（例如平板俯冲、边缘或板块中的扭结）和俯冲相关过程，例如上板块变形、沿俯冲界面的耦合以及瞬态事件（例如慢滑移）。 来自该地区 4 个新的连续 GPS 站点、5 个新的活动站点以及现有的连续和活动站点的数据正在用于检查应变模式、俯冲板块的几何形状、沿俯冲界面的耦合、上部板块运动和瞬态过程沿着阿拉斯加最东部的俯冲带。 该项目正在解决以下问题：1）俯冲界面的几何形状是什么？活动俯冲界面的东边在哪里？这与兰格尔火山场和观测到的地震活动有何关系？ 2）阿拉斯加最东部俯冲带内的耦合如何变化？从锁定到蠕动的转变发生在哪里？这与观测到的震动、上部板块变形和地震活动有何关系？ 3）俯冲界面上是否存在类似慢滑事件的瞬变事件？这些瞬态事件与界面几何形状和耦合分布有何关系？ 新数据允许在比目前更密集的空间和时间尺度上评估板块边界特征，从而为雅库塔特板块界面的行为及其对该地区构造的影响建立更详细和更现实的模型。