Collaborative Research: Incoming plate and forearc structure of the Semidi and SW Kodiak Segments offshore Alaska Peninsula from 3-D active-source and local earthquake tomography

最大的地震和相关的海啸以及火山爆发都发生在俯冲带，一个构造板块潜入另一个构造板块之下。北美的一个突出例子是阿拉斯加半岛近海的俯冲带，在那里发生了一些现代有记录以来最大的地震，比如1938年的大地震和1964年毁灭性的9.2级威廉王子地震。在这个地区，大地震和小地震的历史以及两个板块锁在一起的强度沿着边缘变化很大，变化很快。然而，关于俯冲带产生大地震的能力，许多问题仍未得到解答。该项目将分析和解释地震记录，这些记录是在2018-2019年由NSF-GeoPRISMS资助的阿拉斯加两栖社区地震实验（AACSE）中收集的。由密集的海上和陆上地震仪阵列记录的地震数据，将使这一俯冲带的地质结构和物理特性的三维图像得以发展，其深度可达100公里。图像的质量将足够高，可以用来检查先前提出的结构，以解释该地区和全球其他俯冲带板块边界地震行为的变化。该项目支持培养两名研究生。基于AACSE两栖阵列记录的可控震源和局部地震数据，将进行纵波和横波结构的三维地震层析成像研究。该项目将解决以下关键问题：阿拉斯加半岛边缘的孕震性质、震间期地震活动性和板块耦合在多大程度上受上陆板块构造、组成和/或下行大洋板块物理性质和构造（如海山、弯曲断层和断裂带）的顺走和下倾变化控制？三维地震速度模型将用于研究进入俯冲带的水沿走向的变化，以及假定的水合海洋地幔的深度范围，以及水是否被输送到可能影响大逆冲地震性质的发震深度。通过绘制沿板块界面的地震速度异常，将研究板块界面的起伏和俯冲构造异常（如海山链、膨胀带和断裂带）的存在（或不存在），以及它们在促进破裂分割和大地测量推断的板块界面锁定变化中的假定作用。加深对与大地震相关的俯冲带过程的了解，对于评估阿拉斯加半岛俯冲带的地震和海啸灾害具有重要意义。尽管该项目关注的是阿拉斯加半岛俯冲带，但这个科学问题适用于全球许多俯冲带。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。

The largest earthquakes and associated tsunamis as well as volcanic eruptions are found at subduction zones where one tectonic plate dives beneath another. A prominent example in North America is the subduction zone offshore of the Alaska Peninsula, where some of the largest earthquakes ever recorded in modern times have occurred, like the great earthquake of 1938 and the devastating 1964 M9.2 Prince William earthquake. In this region the history of large and small earthquakes and how strongly the two plates are locked together vary substantially and rapidly along the margin. Many questions, however, remain unanswered about the ability of the subduction zone to generate large earthquakes. This project will analyze and interpret recordings of earthquakes that were collected as part of a larger NSF-GeoPRISMS funded Alaska Amphibious Community Seismic Experiment (AACSE) in 2018-2019. The seismic data, recorded by a dense array of offshore and onshore seismometers, will allow the development of a three-dimensional image of the geological structure and physical properties of this subduction zone down to a depth of 100 km. The quality of the images will be high enough to examine structures that have been previously proposed to explain changes in the seismic behavior of the plate boundary in this area and at other subduction zones worldwide. The project supports the training of two graduate students.Three-dimensional seismic tomography studies will be conducted of P- and S-wave structure based on controlled-source and local earthquake data recorded by the AACSE amphibious array. The project will address the following key question: To what extent is the segmentation of the Alaska Peninsula margin in seismogenic properties, seismicity during the interseismic period, and plate coupling controlled by along-strike and downdip variations in upper continental plate structure, composition, and/or downgoing oceanic plate physical properties and structures such as seamounts, bending faults and fracture zones? The 3-D seismic velocity models will be used to investigate along-strike variations in water input into the subduction zone, as well as depth extent of the presumed hydrated oceanic mantle and whether or not water is delivered to seismogenic depths where it could influence megathrust seismic properties. By mapping seismic velocity anomalies along the plate interface, the plate interface relief and the presence (or lack thereof) of subducted structural anomalies such as seamounts chains, swell and fracture zones, and their presumed role in contributing to rupture segmentation and variations in the geodetically inferred plate interface locking, will be examined. An improved understanding of subduction zone processes associated with large earthquakes is important for assessing earthquakes and tsunami hazards at the Alaska Peninsula subduction zone. Although this project focuses on the Alaska Peninsula subduction zone, the scientific question applies across many subduction zones worldwide.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.