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

阿拉斯加是由夹在亚洲和北美旧大陆地壳之间的地壳碎片组成的。由于板块构造，阿拉斯加继续相对于北美稳定的部分移动。该州大部分地区都有活跃的地震活动，这会在沿海地区产生地震、火山喷发和潜在海啸等灾害。阿拉斯加是由各种各样的地质作用建成的。这使它成为理想的天然实验室。其活跃的南部边缘尤其复杂。在那里，雅库塔特微板块与北美板块相撞；这是阿留申俯冲带太平洋板块俯冲的结果。最近在阿拉斯加各地部署了许多地震仪，这为成像潜在的地质结构提供了前所未有的机会。在这里，该团队开发了新的工具和模型，以3D方式测量地壳和地幔最高处120-150公里的地震速度。根据地震资料建立了一系列模型。它们包括一个各向同性成分，它详细说明了地下结构的几何形状、温度和组成。这些模型还考虑了地震波传播中的方向变化；这提供了关于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了解，包括危及人口中心的大地震。该项目还为几名研究生提供了尖端地震学方面的部分支持和培训。该团队将与科学界共享开发的代码和分析，允许它们应用于世界其他地区。在这里，团队测量环境噪声和地震得出的瑞利波和乐夫波速度，说明它们的方位相关性。研究人员使用接收器函数等补充数据。这有助于产生更精细、更高分辨率的岩石圈模型。新奇之处包括三站干涉测量的应用和倾斜弹性张量的反演。所有数据都是在贝叶斯蒙特卡罗反演的框架内解释的。生成可接受模型的分布，根据该分布估计模型不确定性。科学目标包括(1)成像阿拉斯加南部边缘的逆冲岩石圈以及上覆的地壳和地幔楔形；目标是寻找板片撕裂、平板区、板片边缘和增厚的岩石圈。该团队还研究了阿拉斯加山脉和布鲁克斯山脉下地壳厚度的差异，以及这些山脉和其他山脉均衡补偿的程度。他们寻找(3)俯冲岩石圈边缘的角流各向异性和(4)雅库塔特岩石圈是否与周围地区不同的证据。一个目标也是(5)确定克拉通岩石圈和变形的岩石圈之间的接触几何。地震模型将被存档，并通过IRIS-DMS与更广泛的地球科学界共享。3-D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(过渡到GitHub)的动态更新的开放访问数据库向公众提供。其中包括频散图、接收器函数、面波观测数据(如H/V比)和研究代码。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.