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Seismic Interferometry and Data Assimilation for Lithospheric Structure and Anisotropy Across Alaska

阿拉斯加岩石圈结构和各向异性的地震干涉测量和数据同化

基本信息

批准号：
1928395
负责人：
Michael Ritzwoller
金额：
$ 29.52万
依托单位：
University of Colorado at Boulder
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-09-01 至 2023-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1928395&HistoricalAwards=false
关键词：
Seismic Interferometry Data Assimilation Lithospheric

项目摘要

Alaska is composed of crustal fragments sandwiched in between old continental crusts in Asia and North America. Because of plate tectonics, Alaska continues to move relative to the stable parts of North America. Active seismicity is found across most of the state which generates hazards such as earthquakes, volcanic eruptions, and potential tsunamis in coastal areas. Alaska has been built by a wide variety of geological processes. This makes it an ideal natural laboratory. Its active southern margin is particularly complex. There, the Yakutat microplate collides with the North American plate; a result of the under-thrusting of the Pacific Plate in the Aleutian subduction zone. The recent deployment of numerous seismometers across Alaska provides an unprecedented opportunity to image the underlying geological structures. Here, the team develops new tools and models in 3D the seismic velocities in the crust and uppermost mantle to a depth of 120-150 km. A series of models are generated from the seismic data. They include an isotropic component which details the geometry, temperature and composition of the subsurface structures. The models also account for directional variations in seismic wave propagation; this provides information about past and on-going deformation processes. Outcomes of the project will improve the understanding of seismogenic processes in Alaska, including megathrust earthquakes that endanger the population centers. The project also provides partial support and training in cutting-edge seismology to several graduate students. The team will share the developed codes and analyses with the scientific community, allowing their application to other regions of the World.Here, the team measures the Rayleigh and Love wave velocities derived from ambient noise and earthquakes, accounting for their azimuthally dependence. The researchers use complementary data such as receiver functions. This helps produce more refined, higher resolution lithospheric models. Novelties include the application of three-station interferometry and the inversion for the tilted elastic tensor. All data are interpreted within the framework of a Bayesian Monte Carlo inversion. A distribution of accepted models is generated from which model uncertainties are estimated. Scientific objectives include (1) imaging the under-thrusting lithosphere along Alaska's southern margin as well as the overlying crust and mantle wedge; the goal is to search for slab tears, flat slab regions, slab edges, and thickened lithosphere. The team investigates as well (2) how crustal thickness differs beneath the Alaska and Brooks ranges and to what extent these and other ranges are compensated isostatically. They look for evidence of (3) anisotropy from corner flow around the edges of subducting lithosphere and (4) whether Yakutat lithosphere differs from that of the surrounding regions. One goal is also to (5) determine the geometry of contact between cratonic and deformed lithosphere. The seismological models will be archived and shared with the broader geoscience community via the IRIS-DMS. 3-D models and other higher-level data products are delivered to the public through dynamically updated, open access databases at University of Colorado, Boulder (transitioning to GitHub). These include dispersion maps, receiver functions, surface wave observables like H/V ratios, and research codes.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.

阿拉斯加是由夹在亚洲和北美古老大陆地壳之间的地壳碎片组成的。由于板块构造，阿拉斯加相对于北美的稳定部分继续移动。该州大部分地区都有活跃的地震活动，这会产生地震、火山爆发和沿海地区潜在的海啸等灾害。阿拉斯加是由各种各样的地质作用形成的。这使它成为一个理想的天然实验室。其活跃的南部边缘特别复杂。在那里，雅库塔特微板块与北美板块碰撞;这是太平洋板块在阿留申俯冲带下冲的结果。最近在阿拉斯加各地部署了许多地震仪，这为对底层地质结构进行成像提供了前所未有的机会。在这里，该团队开发了新的工具和3D模型，用于地壳和上地幔的地震速度，深度为120-150公里。从地震数据生成一系列模型。它们包括一个各向同性的组成部分，详细说明了几何形状，温度和地下结构的组成。该模型还考虑了地震波传播的方向变化，这提供了有关过去和正在进行的变形过程的信息。该项目的成果将提高对阿拉斯加地震孕育过程的认识，包括危及人口中心的大推力地震。该项目还为几名研究生提供了部分支持和尖端地震学培训。该团队将与科学界分享开发的代码和分析，使其能够应用于世界其他地区。在这里，该团队测量了来自环境噪声和地震的瑞利波和洛夫波速度，并解释了它们的方位角依赖性。研究人员使用补充数据，如接收器函数。这有助于产生更精细、更高分辨率的岩石圈模型。新颖之处包括应用三站干涉测量和反演倾斜弹性张量。所有数据都在贝叶斯蒙特卡罗反演的框架内进行解释。可接受的模型的分布产生的模型的不确定性估计。科学目标包括（1）成像下逆冲岩石圈沿沿着阿拉斯加的南部边缘以及上覆地壳和地幔楔;目标是寻找板片撕裂，平板区域，板片边缘，和增厚的岩石圈。该小组还调查了阿拉斯加和布鲁克斯山脉下的地壳厚度如何不同，以及这些山脉和其他山脉在何种程度上得到均衡补偿。他们寻找（3）俯冲岩石圈边缘角流的各向异性和（4）雅库特岩石圈是否与周围地区不同的证据。目的之一是（5）确定岩石圈与变形岩石圈接触的几何形状。地震模型将通过IRIS-DMS存档并与更广泛的地球科学界共享。3D模型和其他更高级别的数据产品通过科罗拉多大学博尔德分校的动态更新的开放访问数据库（过渡到GitHub）向公众提供。这一奖项反映了NSF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。