RUI: Lithospheric Velocity Structure and Anisotropy of the Alaskan Subduction Margin

阿拉斯加南部海岸是美国地震和火山活动最活跃的地区，也是地球上有记录以来第二大地震的发生地。然而，地震和火山的行为在沿海地区之间发生了巨大变化。有些地区会发生特大地震，而其他地区只有小到中等规模的地震。同样，火山的化学成分和喷发方式也会沿着海岸变化。了解这些差异的起源可能会导致对全球地震和火山危害的重要见解。科学家们认为，了解这个系统的关键可能在于地表以下100-200公里的岩石结构和流体含量，太平洋构造板块潜入北美构造板块之下。这项研究将利用地震波来拍摄埋在阿拉斯加海岸下的岩石。这些波被称为表面波，在地球表面附近传播，并根据它们所穿过的岩石的特性改变速度。通过测量基于位置和波传播方向的波速差异，我们将研究地震和火山行为的差异是否与(a)岩浆生产区的变化，(b)岩石流体含量的变化，或(c)岩石在地表深处缓慢流动方向的变化有关。这项工作将在一个主要的本科生机构完成，并为本科生提供研究经验。该项目还支持培养一名早期职业博士后研究员。阿拉斯加南缘的俯冲带是许多活火山的所在地，也是美国地震最活跃的地区。它曾发生过几次大型逆冲地震，包括1964年的阿拉斯加大地震，这是有记录以来的第二大地震。然而，俯冲带的地震和火山活动沿着走向经历了剧烈的变化，一些地区在大（M8）事件中滑动，而其他地区主要通过蠕变变形。了解这种变化的起源可以对俯冲带过程和全球地球物理危害有重要的认识。近年来的研究表明，俯冲板块和地幔楔的水化作用可能在控制这些行为方面起着重要作用。在本研究中，将利用最近从阿拉斯加两栖社区地震实验和阿拉斯加可移动阵列收集的数据来建立Rayleigh和Love波速模型，并求解阿拉斯加俯冲带下上地幔剪切波的径向和方位各向异性。这些速度模型将用于确定弧前地幔结构、进入板块和地幔楔的水化作用以及地幔流动如何共同影响沿俯冲带的火山和地震行为。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 southern coast of Alaska is the most seismically and volcanically active portion of the United States, and was home to the second largest earthquake recorded anywhere on Earth. The behavior of earthquakes and volcanos, however, changes dramatically between regions along the coast. Some areas produce extremely large earthquakes, while other regions have only small to moderate-sized earthquakes. Similarly, the chemistry and eruption styles of volcanos change along the coast. Understanding the origins of these differences could lead to important insights into global earthquake and volcano hazards. Scientists believe that the key to understanding this system may lie in the structure and fluid-content of rocks 100-200 km beneath the surface, where the Pacific tectonic plate dives beneath the North America tectonic plate. This study will use earthquake waves to image these rocks buried under Alaska’s coast. These waves, called surface waves, travel across the earth near the surface and change speeds based on the characteristics of the rocks that they travel through. By measuring differences in wave speed based on location and the direction the waves travel, we will examine whether differences in earthquake and volcano behavior are connected to (a) changes in magma-production regions, (b) changes in the fluid content of rocks, or (c) changes in the direction that rocks slowly flow deep beneath the surface. The work will be completed at a Primarily Undergaduate Institution and provides research experience for undergraduate students. The project also supports the training of an early career Postdoctoral Investigator.The subduction zone along the southern margin of Alaska is home to numerous active volcanos, and is the most seismically active portion of the United States. It has hosted several megathrust earthquakes, including the 1964 Great Alaskan Earthquake, the second largest earthquake in recorded history. The seismic and volcanic behavior of the subduction zone, however, undergoes dramatic changes along strike, with some areas slipping in great (M8) events while other regions deform primarily through creep. Understanding the origins of this variability could lead to important insights into subduction zone processes and global geophysical hazards. Recent studies have highlighted the role that hydration of the subducting slab and the mantle wedge may play in governing these behaviors. In this study, recently collected data from the Alaska Amphibious Community Seismic Experiment and the Alaska Transportable Array will be leveraged to build Rayleigh and Love wave velocity models and to solve for radial and azimuthal anisotropy of shear waves in the upper mantle beneath the Alaskan subduction zone. These velocity models will be used to determine how forearc mantle structure, hydration of the incoming plate and the mantle wedge, and mantle flow combine to influence volcanic and seismic behavior along the subduction zone.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.