EAR-PF: A Multiscale Seismic Velocity Model for the Gulf of Alaska

Evans Onyango获得了NSF的博士后奖学金，以开展与开发阿拉斯加湾多尺度地震速度模型相关的研究和教育活动。这项工作将在阿拉斯加大学费尔班克斯的指导下进行。地球的表面被划分为多个板块，这些板块在不断运动，并沿着板块之间的边界沿着相互碰撞、滑过或拉开。板块的相互作用形成山脉，引起火山活动，并产生大地震。阿拉斯加是世界上地震最活跃的板块边界之一，1964年发生了美国有史以来最大的9.2级地震。科学家们依靠地球地下物质的三维模型来了解板块构造过程和评估地质灾害。为了更好地了解大地震，科学家必须了解地震波如何与地球的地下物质相互作用。阿拉斯加南部地震波场建模的一个主要限制是缺乏三维海上模型。永久性地震台站位于陆地上，远离近海地震，这使得难以模拟沿海城市的地面运动。该项目旨在建立和测试阿拉斯加湾的三维地下模型，以更好地了解沿海地区复杂的地震地面运动。我们的目标是通过结合现有的二维模型从以前的研究创建一个全面的三维模型。将对这一模型内的地震波传播进行计算机模拟，以生成预测的地震图，并将其与该区域中等地震的记录地震图进行比较。最终的模型将通过IRIS地球模型合作组织公开访问，这是一个地球模型的公共存储库。该项目将涉及向容易遭受地震和海啸危险的当地沿海社区进行宣传，位于构造活动边缘的近海地区，如阿拉斯加南部或加州南部，往往具有极端复杂的结构，并在震级和机制方面产生各种各样的地震。在阿拉斯加南部，雅库塔特微板块在北美板块之下的活跃碰撞和增生，以及在这一活跃俯冲带的增生楔的结构，都是造成该地区复杂结构的因素的例子。小规模和大规模部署的地震仪器在陆地上，如EarthScope便携式阵列产生了许多阿拉斯加大陆的层析成像模型，其中大多数包括固有的平滑，无法捕捉到尖锐的界面的海上设置。相比之下，阿拉斯加湾的近海区域仅使用20世纪80年代至21世纪初海洋研究中获得的高分辨率2D速度模型进行了研究。该项目建议利用这些来自阿拉斯加湾的现有图像来创建一个全面的3D速度模型，该模型将具有许多用途，例如建模地震波场，了解活动构造以及建模俯冲系统的地球动力学。从所得的3D模型计算的合成波形将与从研究区域的中、大地震记录的地震图进行比较，以验证模型。地震图失配值也将与其他可用的层析成像模型的性能进行比较。该项目将为阿拉斯加湾开发一个3D速度模型，该模型将通过IRIS地球模型协作公开访问，地球模型的公共知识库。该项目由地球科学博士后奖学金计划和刺激竞争性研究的既定计划（EPSCoR）共同资助该奖项反映了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。

Evans Onyango has been awarded an NSF EAR Postdoctoral Fellowship to conduct research and education activities related to developing a multiscale seismic velocity model for the Gulf of Alaska. This work will take place at the University of Alaska Fairbanks under the mentorship of Dr. Carl Tape. The surface of the Earth is divided into plates that are in constant motion and collide, slide past, or pull away from each other along the boundaries between plates. Plate interactions build mountains, cause volcanic activity, and produce large earthquakes. Alaska hosts one of the world’s most seismically active plate boundaries, which produced the 1964 magnitude 9.2 earthquake, the largest ever recorded in the United States. Scientists rely on three-dimensional models of Earth’s subsurface material to understand plate tectonic processes and to assess geologic hazards. In order to better understand large earthquakes, scientists must understand how seismic waves interact with Earth’s subsurface materials. A primary limitation to modeling the seismic wavefield in southern Alaska is the lack of a three-dimensional offshore model. Permanent seismic stations are on land, far from offshore earthquakes, which makes it difficult to model ground motion at coastal cities. This project seeks to build and test a three-dimensional subsurface model for the Gulf of Alaska to better understand the complex earthquake ground motion in coastal regions. The goal is to create a comprehensive three-dimensional model by combining existing two-dimensional models from previous studies. Computer simulations of seismic wave propagation within this model will be performed to generate predicted seismograms that will be compared with recorded seismograms from moderate earthquakes in the region. The final model will be publicly accessible via the IRIS Earth Model Collaboration, a public repository for Earth models. The project will involve outreach to local coastal communities prone to seismic and tsunami hazards.Offshore regions at tectonically active margins, such as southern Alaska or southern California, often exhibit extreme structural complexity and produce a wide range of earthquakes in terms of magnitudes and mechanisms. In southern Alaska, the active collision and accretion of the Yakutat microplate beneath the North America plate and the structure of the accretionary wedge at this active subduction zone are examples of factors contributing to the complex structure of the region. Small-scale and large-scale deployments of seismic instruments on land such as the EarthScope Transportable Array have yielded numerous tomographic models of the mainland Alaska, most of which include inherent smoothing that cannot capture the sharp interfaces of the offshore setting. By comparison, the offshore region of the Gulf of Alaska has only been studied with a sparse assortment of high-resolution 2D velocity models derived from marine studies between the 1980s and 2000s. This project proposes leveraging these existing images from the Gulf of Alaska to create a comprehensive 3D velocity model that will have many uses such as modeling the seismic wavefield, understanding active tectonics, and modeling geodynamics of the subduction system. Synthetic waveforms calculated from the resultant 3D model will be compared with seismograms recorded from moderate and large earthquakes in the study area to validate the model. Seismogram misfit values will also be compared with the performance of other available tomographic models. This project will develop a 3D velocity model for the Gulf of Alaska that will be publicly accessible via the IRIS Earth Model Collaboration, a public repository for Earth models.This project is jointly funded by the Earth Sciences Postdoctoral Fellowship program and the Established Program to Stimulate Competitive Research (EPSCoR).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.