Geodetic Characterization of the Easternmost Alaska Subduction Zone

非技术摘要俯冲带，一个构造板块下沉到另一个板块之下，会产生大地震，因此构成重大的地震危险。了解板块的特征，如下降板块(或板块)的几何形状，以及它们相互滑动的过程，是评估地震风险程度的关键。两个板块的一部分或全部可能粘在一起，累积的应变可能会在大地震中释放出来，或者它们可能会更安静地彼此滑动，包括在“慢滑事件”中，能量在几天或几年而不是几秒钟内释放。阿拉斯加中南部是研究板块和上板块特征与俯冲带滑动行为之间联系的极好实验室。该地区发生了有记录以来第二大地震(1964年发生9.2级)，但关于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的下方。这次地震活动在发生9.2级地震的地方以东突然停止，导致人们猜测该板块可能不会在整个地区连续。最近的GPS研究表明，该板块存在，并与上板块锁定在该地区的大部分地区，地震调查发现也可能发生瞬变行为，但稀少的数据限制了进一步的工作。来自普渡大学的项目组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结合起来，以研究该地区的俯冲过程，包括了解板块和上板块的几何形状，并确定板块锁定的位置和程度。该团队还在寻找瞬变事件的微妙证据；如果发现，这些事件可能与板块几何形状和板块锁定有关。该项目还为当地的K-12教师提供了参与实地工作的机会，并了解GPS数据如何用于构造研究。与这些教师一起制定的教案将该项目的研究纳入了对该地区构造的更大范围的看法，并给学生提供了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，将其研究成果传播给更多的受众。总体而言，该项目正在产生和传达对阿拉斯加最东端俯冲带过程的更全面的理解，这将改进地震危险性估计。技术描述本提案旨在提高对复杂的板块几何形状(例如平板俯冲、板块中的边缘或扭结)和与俯冲相关的过程之间的关系的理解，例如上板块变形、沿俯冲界面的耦合和瞬变事件(例如慢滑)。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被用来检查应变模式、俯冲板块的几何形状、沿俯冲界面的耦合、上板块运动以及沿阿拉斯加最东端俯冲带的瞬变过程。该项目正在解决以下问题：1)俯冲界面的几何形状是什么？活动俯冲界面的东缘在哪里？这与兰格尔火山场和观测到的地震活动有何关系？2)阿拉斯加最东端俯冲带内的耦合如何变化？从锁定到爬行的转变发生在哪里？这与观测到的震动、上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于慢滑事件的瞬变事件？这些瞬变事件与界面几何形状和耦合分布有何关系？新的数据使得能够在比目前更密集的空间和时间尺度上评估板块边界特征，从而产生更详细和更真实的雅库塔特板块界面行为及其对该地区构造的影响的模型。

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.